Xiaolin Wu's line algorithm: Difference between revisions
→{{header|J}}: use isidraw in j802 |
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const |
const |
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FPS=1000 div 60; |
FPS = 1000 div 60; |
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SCALE=6; |
SCALE = 6; |
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var |
var |
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origin: TSDL_Point; |
origin: TSDL_Point; |
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event: TSDL_Event; |
event: TSDL_Event; |
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line_alpha: byte=255; |
line_alpha: byte = 255; |
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procedure SDL_RenderDrawWuLine(renderer: PSDL_Renderer; x1, y1, x2, y2: longint); |
procedure SDL_RenderDrawWuLine(renderer: PSDL_Renderer; x1, y1, x2, y2: longint); |
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tmp: longint; |
tmp: longint; |
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begin |
begin |
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tmp:=a; |
tmp := a; |
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a:=b; |
a := b; |
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b:=tmp; |
b := tmp; |
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end; |
end; |
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begin |
begin |
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if a=0 then |
if a = 0 then |
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exit; |
exit; |
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SDL_GetRenderDrawColor(renderer, @r, @g, @b, @a); |
SDL_GetRenderDrawColor(renderer, @r, @g, @b, @a); |
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if abs(y2-y1)>abs(x2-x1) then |
if abs(y2 - y1) > abs(x2 - x1) then |
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begin |
begin |
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swap(x1, y1); |
swap(x1, y1); |
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swap(x2, y2); |
swap(x2, y2); |
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px:=@y; |
px := @y; |
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py:=@x; |
py := @x; |
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end |
end |
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else |
else |
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begin |
begin |
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px:=@x; |
px := @x; |
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py:=@y; |
py := @y; |
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end; |
end; |
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if x1>x2 then |
if x1 > x2 then |
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begin |
begin |
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swap(x1, x2); |
swap(x1, x2); |
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swap(y1, y2); |
swap(y1, y2); |
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end; |
end; |
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x:=x2-x1; |
x := x2 - x1; |
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if x=0 then |
if x = 0 then |
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x:=1; |
x := 1; |
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gradient:=(y2-y1)/x; |
gradient := (y2 - y1) / x; |
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iy:=y1; |
iy := y1; |
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for x:=x1 to x2 do |
for x := x1 to x2 do |
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begin |
begin |
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a_new:=round(a*frac(iy)); |
a_new := round(a * frac(iy)); |
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y:=floor(iy); |
y := floor(iy); |
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SDL_SetRenderDrawColor(renderer, r, g, b, a-a_new); |
SDL_SetRenderDrawColor(renderer, r, g, b, a-a_new); |
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SDL_RenderDrawPoint(renderer, px^, py^); |
SDL_RenderDrawPoint(renderer, px^, py^); |
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SDL_SetRenderDrawColor(renderer, r, g, b, a_new); |
SDL_SetRenderDrawColor(renderer, r, g, b, a_new); |
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SDL_RenderDrawPoint(renderer, px^, py^); |
SDL_RenderDrawPoint(renderer, px^, py^); |
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iy:=iy+gradient; |
iy := iy + gradient; |
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end; |
end; |
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SDL_SetRenderDrawColor(renderer, r, g, b, a); |
SDL_SetRenderDrawColor(renderer, r, g, b, a); |
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Line 660: | Line 660: | ||
begin |
begin |
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SDL_Init(SDL_INIT_VIDEO); |
SDL_Init(SDL_INIT_VIDEO); |
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win:=SDL_CreateWindow('Xiaolin Wu''s line algorithm', SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, |
win := SDL_CreateWindow('Xiaolin Wu''s line algorithm', SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, |
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640, 480, SDL_WINDOW_RESIZABLE); |
640, 480, SDL_WINDOW_RESIZABLE); |
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ren:=SDL_CreateRenderer(win, -1, 0); |
ren := SDL_CreateRenderer(win, -1, 0); |
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if ren=NIL then |
if ren = NIL then |
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begin |
begin |
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writeln(SDL_GetError); |
writeln(SDL_GetError); |
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SDL_SetCursor(SDL_CreateSystemCursor(SDL_SYSTEM_CURSOR_CROSSHAIR)); |
SDL_SetCursor(SDL_CreateSystemCursor(SDL_SYSTEM_CURSOR_CROSSHAIR)); |
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mouse_x:=0; |
mouse_x := 0; |
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mouse_y:=0; |
mouse_y := 0; |
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origin.x:=0; |
origin.x := 0; |
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origin.y:=0; |
origin.y := 0; |
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repeat |
repeat |
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while SDL_PollEvent(@event)=1 do |
while SDL_PollEvent(@event) = 1 do |
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case event.type_ of |
case event.type_ of |
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SDL_KEYDOWN: |
SDL_KEYDOWN: |
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if event.key.keysym.sym=SDLK_ESCAPE then |
if event.key.keysym.sym = SDLK_ESCAPE then |
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halt; |
halt; |
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SDL_MOUSEBUTTONDOWN: |
SDL_MOUSEBUTTONDOWN: |
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begin |
begin |
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origin.x:=mouse_x; |
origin.x := mouse_x; |
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origin.y:=mouse_y; |
origin.y := mouse_y; |
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end; |
end; |
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SDL_MOUSEMOTION: |
SDL_MOUSEMOTION: |
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with event.motion do |
with event.motion do |
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begin |
begin |
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mouse_x:=x div SCALE; |
mouse_x := x div SCALE; |
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mouse_y:=y div SCALE; |
mouse_y := y div SCALE; |
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end; |
end; |
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SDL_MOUSEWHEEL: |
SDL_MOUSEWHEEL: |
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line_alpha:=EnsureRange(line_alpha+event.wheel.y*20, 0, 255); |
line_alpha := EnsureRange(line_alpha + event.wheel.y * 20, 0, 255); |
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SDL_QUITEV: |
SDL_QUITEV: |
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halt; |
halt; |
Revision as of 17:54, 10 October 2014
![Task](http://static.miraheze.org/rosettacodewiki/thumb/b/ba/Rcode-button-task-crushed.png/64px-Rcode-button-task-crushed.png)
You are encouraged to solve this task according to the task description, using any language you may know.
Implement the Xiaolin Wu's line algorithm as described in Wikipedia. This algorithm draw antialiased lines. See Bresenham's line algorithm for aliased lines.
BBC BASIC
<lang bbcbasic> PROCdrawAntiAliasedLine(100, 100, 600, 400, 0, 0, 0)
END DEF PROCdrawAntiAliasedLine(x1, y1, x2, y2, r%, g%, b%) LOCAL dx, dy, xend, yend, grad, yf, xgap, ix1%, iy1%, ix2%, iy2%, x% dx = x2 - x1 dy = y2 - y1 IF ABS(dx) < ABS(dy) THEN SWAP x1, y1 SWAP x2, y2 SWAP dx, dy ENDIF IF x2 < x1 THEN SWAP x1, x2 SWAP y1, y2 ENDIF grad = dy / dx xend = INT(x1 + 0.5) yend = y1 + grad * (xend - x1) xgap = xend + 0.5 - x1 ix1% = xend iy1% = INT(yend) PROCplot(ix1%, iy1%, r%, b%, g%, (INT(yend) + 1 - yend) * xgap) PROCplot(ix1%, iy1% + 1, r%, b%, g%, (yend - INT(yend)) * xgap) yf = yend + grad xend = INT(x2 + 0.5) yend = y2 + grad * (xend - x2) xgap = x2 + 0.5 - xend ix2% = xend iy2% = INT(yend) PROCplot(ix2%, iy2%, r%, b%, g%, (INT(yend) + 1 - yend) * xgap) PROCplot(ix2%, iy2% + 1, r%, b%, g%, (yend - INT(yend)) * xgap) FOR x% = ix1% + 1 TO ix2% - 1 PROCplot(x%, INT(yf), r%, b%, g%, INT(yf) + 1 - yf) PROCplot(x%, INT(yf) + 1, r%, b%, g%, yf - INT(yf)) yf += grad NEXT ENDPROC DEF PROCplot(X%, Y%, R%, G%, B%, a) LOCAL C% C% = TINT(X%*2,Y%*2) COLOUR 1, R%*a + (C% AND 255)*(1-a), \ \ G%*a + (C% >> 8 AND 255)*(1-a), \ \ B%*a + (C% >> 16 AND 255)*(1-a) GCOL 1 LINE X%*2, Y%*2, X%*2, Y%*2 ENDPROC</lang>
C
This implementation follows straightforwardly the pseudocode given on Wikipedia. (Further analysis of the code could give suggestions for improvements).
<lang c>void draw_line_antialias(
image img, unsigned int x0, unsigned int y0, unsigned int x1, unsigned int y1, color_component r, color_component g, color_component b );</lang>
<lang c>inline void _dla_changebrightness(rgb_color_p from, rgb_color_p to, float br) {
if ( br > 1.0 ) br = 1.0; /* linear... Maybe something more complex could give better look */ to->red = br * (float)from->red; to->green = br * (float)from->green; to->blue = br * (float)from->blue;
}
- define plot_(X,Y,D) do{ rgb_color f_; \
f_.red = r; f_.green = g; f_.blue = b; \ _dla_plot(img, (X), (Y), &f_, (D)) ; }while(0)
inline void _dla_plot(image img, int x, int y, rgb_color_p col, float br) {
rgb_color oc; _dla_changebrightness(col, &oc, br); put_pixel_clip(img, x, y, oc.red, oc.green, oc.blue);
}
- define ipart_(X) ((int)(X))
- define round_(X) ((int)(((double)(X))+0.5))
- define fpart_(X) (((double)(X))-(double)ipart_(X))
- define rfpart_(X) (1.0-fpart_(X))
- define swap_(a, b) do{ __typeof__(a) tmp; tmp = a; a = b; b = tmp; }while(0)
void draw_line_antialias(
image img, unsigned int x1, unsigned int y1, unsigned int x2, unsigned int y2, color_component r, color_component g, color_component b )
{
double dx = (double)x2 - (double)x1; double dy = (double)y2 - (double)y1; if ( fabs(dx) > fabs(dy) ) { if ( x2 < x1 ) { swap_(x1, x2); swap_(y1, y2); } double gradient = dy / dx; double xend = round_(x1); double yend = y1 + gradient*(xend - x1); double xgap = rfpart_(x1 + 0.5); int xpxl1 = xend; int ypxl1 = ipart_(yend); plot_(xpxl1, ypxl1, rfpart_(yend)*xgap); plot_(xpxl1, ypxl1+1, fpart_(yend)*xgap); double intery = yend + gradient;
xend = round_(x2); yend = y2 + gradient*(xend - x2); xgap = fpart_(x2+0.5); int xpxl2 = xend; int ypxl2 = ipart_(yend); plot_(xpxl2, ypxl2, rfpart_(yend) * xgap); plot_(xpxl2, ypxl2 + 1, fpart_(yend) * xgap);
int x; for(x=xpxl1+1; x <= (xpxl2-1); x++) { plot_(x, ipart_(intery), rfpart_(intery)); plot_(x, ipart_(intery) + 1, fpart_(intery)); intery += gradient; } } else { if ( y2 < y1 ) { swap_(x1, x2); swap_(y1, y2); } double gradient = dx / dy; double yend = round_(y1); double xend = x1 + gradient*(yend - y1); double ygap = rfpart_(y1 + 0.5); int ypxl1 = yend; int xpxl1 = ipart_(xend); plot_(xpxl1, ypxl1, rfpart_(xend)*ygap); plot_(xpxl1, ypxl1+1, fpart_(xend)*ygap); double interx = xend + gradient;
yend = round_(y2); xend = x2 + gradient*(yend - y2); ygap = fpart_(y2+0.5); int ypxl2 = yend; int xpxl2 = ipart_(xend); plot_(xpxl2, ypxl2, rfpart_(xend) * ygap); plot_(xpxl2, ypxl2 + 1, fpart_(xend) * ygap);
int y; for(y=ypxl1+1; y <= (ypxl2-1); y++) { plot_(ipart_(interx), y, rfpart_(interx)); plot_(ipart_(interx) + 1, y, fpart_(interx)); interx += gradient; } }
}
- undef swap_
- undef plot_
- undef ipart_
- undef fpart_
- undef round_
- undef rfpart_</lang>
D
This performs the mixing of the colors, both in grey scale and RGB. <lang d>import std.math, std.algorithm, grayscale_image;
/// Plots anti-aliased line by Xiaolin Wu's line algorithm. void aaLine(Color)(ref Image!Color img,
double x1, double y1, double x2, double y2, in Color color) pure nothrow @safe @nogc { // Straight translation of Wikipedia pseudocode.
// std.math.round is not pure. ** static double round(in double x) pure nothrow @safe @nogc { return floor(x + 0.5); }
static double fpart(in double x) pure nothrow @safe @nogc { return x - x.floor; }
static double rfpart(in double x) pure nothrow @safe @nogc { return 1 - fpart(x); }
auto dx = x2 - x1; auto dy = y2 - y1; immutable ax = dx.abs; immutable ay = dy.abs;
static Color mixColors(in Color c1, in Color c2, in double p) pure nothrow @safe @nogc { static if (is(Color == RGB)) return Color(cast(ubyte)(c1.r * p + c2.r * (1 - p)), cast(ubyte)(c1.g * p + c2.g * (1 - p)), cast(ubyte)(c1.b * p + c2.b * (1 - p))); else // This doesn't work for every kind of Color. return Color(cast(ubyte)(c1 * p + c2 * (1 - p))); }
// Plot function set here to handle the two cases of slope. void function(ref Image!Color, in int, in int, in double, in Color) pure nothrow @safe @nogc plot;
if (ax < ay) { swap(x1, y1); swap(x2, y2); swap(dx, dy); //plot = (img, x, y, p, col) { plot = (ref img, x, y, p, col) { assert(p >= 0.0 && p <= 1.0); img[y, x] = mixColors(col, img[y, x], p); }; } else { //plot = (img, x, y, p, col) { plot = (ref img, x, y, p, col) { assert(p >= 0.0 && p <= 1.0); img[x, y] = mixColors(col, img[x, y], p); }; }
if (x2 < x1) { swap(x1, x2); swap(y1, y2); } immutable gradient = dy / dx;
// Handle first endpoint. auto xEnd = round(x1); auto yEnd = y1 + gradient * (xEnd - x1); auto xGap = rfpart(x1 + 0.5); // This will be used in the main loop. immutable xpxl1 = cast(int)xEnd; immutable ypxl1 = cast(int)yEnd.floor; plot(img, xpxl1, ypxl1, rfpart(yEnd) * xGap, color); plot(img, xpxl1, ypxl1 + 1, fpart(yEnd) * xGap, color); // First y-intersection for the main loop. auto yInter = yEnd + gradient;
// Handle second endpoint. xEnd = round(x2); yEnd = y2 + gradient * (xEnd - x2); xGap = fpart(x2 + 0.5); // This will be used in the main loop. immutable xpxl2 = cast(int)xEnd; immutable ypxl2 = cast(int)yEnd.floor; plot(img, xpxl2, ypxl2, rfpart(yEnd) * xGap, color); plot(img, xpxl2, ypxl2 + 1, fpart(yEnd) * xGap, color);
// Main loop. foreach (immutable x; xpxl1 + 1 .. xpxl2) { plot(img, x, cast(int)yInter.floor, rfpart(yInter), color); plot(img, x, cast(int)yInter.floor + 1, fpart(yInter), color); yInter += gradient; }
}
void main() {
auto im1 = new Image!Gray(400, 300); im1.clear(Gray.white); im1.aaLine(7.4, 12.3, 307, 122.5, Gray.black); im1.aaLine(177.4, 12.3, 127, 222.5, Gray.black); im1.savePGM("xiaolin_lines1.pgm");
auto im2 = new Image!RGB(400, 300); im2.clear(RGB(0, 255, 0)); immutable red = RGB(255, 0, 0); im2.aaLine(7.4, 12.3, 307, 122.5, red); im2.aaLine(177.4, 12.3, 127, 222.5, red); im2.savePPM6("xiaolin_lines2.ppm");
}</lang>
Go
<lang go>package raster
import "math"
func ipart(x float64) float64 {
return math.Floor(x)
}
func round(x float64) float64 {
return ipart(x + .5)
}
func fpart(x float64) float64 {
return x - ipart(x)
}
func rfpart(x float64) float64 {
return 1 - fpart(x)
}
// AaLine plots anti-aliased line by Xiaolin Wu's line algorithm. func (g *Grmap) AaLine(x1, y1, x2, y2 float64) {
// straight translation of WP pseudocode dx := x2 - x1 dy := y2 - y1 ax := dx if ax < 0 { ax = -ax } ay := dy if ay < 0 { ay = -ay } // plot function set here to handle the two cases of slope var plot func(int, int, float64) if ax < ay { x1, y1 = y1, x1 x2, y2 = y2, x2 dx, dy = dy, dx plot = func(x, y int, c float64) { g.SetPx(y, x, uint16(c*math.MaxUint16)) } } else { plot = func(x, y int, c float64) { g.SetPx(x, y, uint16(c*math.MaxUint16)) } } if x2 < x1 { x1, x2 = x2, x1 y1, y2 = y2, y1 } gradient := dy / dx
// handle first endpoint xend := round(x1) yend := y1 + gradient*(xend-x1) xgap := rfpart(x1 + .5) xpxl1 := int(xend) // this will be used in the main loop ypxl1 := int(ipart(yend)) plot(xpxl1, ypxl1, rfpart(yend)*xgap) plot(xpxl1, ypxl1+1, fpart(yend)*xgap) intery := yend + gradient // first y-intersection for the main loop
// handle second endpoint xend = round(x2) yend = y2 + gradient*(xend-x2) xgap = fpart(x2 + 0.5) xpxl2 := int(xend) // this will be used in the main loop ypxl2 := int(ipart(yend)) plot(xpxl2, ypxl2, rfpart(yend)*xgap) plot(xpxl2, ypxl2+1, fpart(yend)*xgap)
// main loop for x := xpxl1 + 1; x <= xpxl2-1; x++ { plot(x, int(ipart(intery)), rfpart(intery)) plot(x, int(ipart(intery))+1, fpart(intery)) intery = intery + gradient }
}</lang> Demonstration program: <lang go>package main
// Files required to build supporting package raster are found in: // * This task (immediately above) // * Bitmap // * Grayscale image // * Write a PPM file
import "raster"
func main() {
g := raster.NewGrmap(400, 300) g.AaLine(7.4, 12.3, 307, 122.5) g.AaLine(177.4, 12.3, 127, 222.5) g.Bitmap().WritePpmFile("wu.ppm")
}</lang>
J
Solution: <lang j>load'gl2' coinsert'jgl2'
drawpt=:4 :0"0 1
glrgb <.(-.x)*255 255 255 glpixel y
)
drawLine=:3 :0 NB. drawline x1,y1,x2,y2
pts=. 2 2$y isreversed=. </ |d=. -~/pts r=. |.^:isreversed"1 pts=. /:~ pts \:"1 |d gradient=. %~/ (\:|)d
'x y'=. |:pts xend=. <.0.5+ x yend=. y + gradient* xend-x xgap=. -.1|x+0.5
n=. i. >: -~/ xend 'xlist ylist'=. (n*/~1,gradient) + ({.xend),({.yend) weights=. ((2&}.,~ xgap*2&{.)&.(_1&|.) (,.~-.) 1|ylist) weights (drawpt r)"1 2 (,:+&0 1)"1 xlist,.<.ylist
)</lang>
Example use: <lang j> wd'pc win closeok; xywh 0 0 300 200;cc g isigraph; pas 0 0; pshow;' NB. J6 or earlier
wd'pc win closeok; minwh 600 400;cc g isidraw flush; pshow;' NB. J802 or later glpaint glclear glpaint drawLine 10 10 590 390</lang>
Liberty BASIC
<lang lb> NoMainWin WindowWidth = 270 WindowHeight = 290 UpperLeftX=int((DisplayWidth-WindowWidth)/2) UpperLeftY=int((DisplayHeight-WindowHeight)/2)
Global variablesInitialized : variablesInitialized = 0 Global BackColor$ : BackColor$ = "0 0 0" ' BackColor$ = "255 255 255"
'now, right click randomizes BG
Global size : size = 1'4 global mousepoints.mouseX0, mousepoints.mouseY0, mousepoints.mouseX1, mousepoints.mouseY1
'StyleBits #main.gbox, 0, _WS_BORDER, 0, 0 GraphicBox #main.gbox, 0, 0, 253, 252
Open "Click Twice to Form Line" For Window As #main Print #main, "TrapClose quit" Print #main.gbox, "Down; Color Black" Print #main.gbox, "Down; fill ";BackColor$ Print #main.gbox, "When leftButtonUp gBoxClick" Print #main.gbox, "When rightButtonUp RandomBG" Print #main.gbox, "Size "; size
result = drawAntiAliasedLine(126.5, 0, 126.5, 252, "255 0 0") result = drawAntiAliasedLine(0, 126, 253, 126, "255 0 0") result = drawAntiAliasedLine(0, 0, 253, 252, "255 0 0") result = drawAntiAliasedLine(253, 0, 0, 252, "255 0 0") Wait
Sub quit handle$ Close #main End End Sub
sub RandomBG handle$, MouseX, MouseY
BackColor$ = int(rnd(1)*256);" ";int(rnd(1)*256);" ";int(rnd(1)*256) Print #main.gbox, "CLS; fill ";BackColor$ variablesInitialized = 0
end sub
Sub gBoxClick handle$, MouseX, MouseY 'We will use the mousepoints "struct" to hold the values 'that way they are retained between subroutine calls If variablesInitialized = 0 Then Print #main.gbox, "CLS; fill ";BackColor$ mousepoints.mouseX0 = MouseX mousepoints.mouseY0 = MouseY variablesInitialized = 1 Else If variablesInitialized = 1 Then mousepoints.mouseX1 = MouseX mousepoints.mouseY1 = MouseY variablesInitialized = 0 result = drawAntiAliasedLine(mousepoints.mouseX0, mousepoints.mouseY0, mousepoints.mouseX1, mousepoints.mouseY1, "255 0 0") End If End If End Sub
Function Swap(Byref a,Byref b) aTemp = b b = a a = aTemp End Function
Function RoundtoInt(val) RoundtoInt = Int(val + 0.5) End Function
Function PlotAntiAliased(x, y, RGB$, b, steep)
RGB$ = Int(Val(Word$(BackColor$, 1))*(1-b) + Val(Word$(RGB$, 1)) * b) ; " " ; _ Int(Val(Word$(BackColor$, 2))*(1-b) + Val(Word$(RGB$, 3)) * b) ; " " ; _ Int(Val(Word$(BackColor$, 3))*(1-b) + Val(Word$(RGB$, 2)) * b)
if steep then 'x and y reversed Print #main.gbox, "Down; Color " + RGB$ + "; Set " + str$(y) + " " + str$(x) else Print #main.gbox, "Down; Color " + RGB$ + "; Set " + str$(x) + " " + str$(y) end if End Function
Function fracPart(x) fracPart = (x Mod 1) End function
Function invFracPart(x) invFracPart = (1 - fracPart(x)) End Function
Function drawAntiAliasedLine(x1, y1, x2, y2, RGB$) If (x2 - x1)=0 Or (y2 - y1)=0 Then Print #main.gbox, "Down; Color " + RGB$ result = BresenhamLine(x1, y1, x2, y2) Exit Function End If steep = abs(x2 - x1) < abs(y2 - y1) if steep then 'x and y should be reversed result = Swap(x1, y1) result = Swap(x2, y2) end if
If (x2 < x1) Then result = Swap(x1, x2) result = Swap(y1, y2) End If dx = (x2 - x1) dy = (y2 - y1) grad = (dy/ dx) 'Handle the First EndPoint xend = RoundtoInt(x1) yend = y1 + grad * (xend - x1) xgap = invFracPart(x1 + 0.5) ix1 = xend iy1 = Int(yend) result = PlotAntiAliased(ix1, iy1, RGB$, invFracPart(yend) * xgap, steep ) result = PlotAntiAliased(ix1, (iy1 + size), RGB$, fracPart(yend) * xgap, steep ) yf = (yend + grad) 'Handle the Second EndPoint xend = RoundtoInt(x2) yend = y2 + grad * (xend - x2) xgap = fracPart(x2 + 0.5) ix2 = xend iy2 = Int(yend) result = PlotAntiAliased(ix2, iy2, RGB$, invFracPart(yend) * xgap, steep ) result = PlotAntiAliased(ix2, (iy2 + size), RGB$, fracPart(yend) * xgap, steep ) For x = ix1 + 1 To ix2 - 1 result = PlotAntiAliased(x, Int(yf), RGB$, invFracPart(yf), steep ) result = PlotAntiAliased(x, (Int(yf) + size), RGB$, fracPart(yf), steep ) yf = (yf + grad) Next x End Function
Function BresenhamLine(x0, y0, x1, y1) dx = Abs(x1 - x0) dy = Abs(y1 - y0) sx = ((x1 > x0) + Not(x0 < x1)) sy = ((y1 > y0) + Not(y0 < y1)) errornum = (dx - dy) Do While 1 Print #main.gbox, "Set " + str$(x0) + " " + str$(y0) If (x0 = x1) And (y0 = y1) Then Exit Do errornum2 = (2 * errornum) If errornum2 > (-1 * dy) Then errornum = (errornum - dy) x0 = (x0 + sx) End If If errornum2 < dx Then errornum = (errornum + dx) y0 = (y0 + sy) End If Loop End Function
</lang>
Pascal
Based on Wikipwdia pseudocode with some optimizations and alpha handling.
<lang pascal> program wu; uses
SDL2, math;
const
FPS = 1000 div 60; SCALE = 6;
var
win: PSDL_Window; ren: PSDL_Renderer; mouse_x, mouse_y: longint; origin: TSDL_Point; event: TSDL_Event; line_alpha: byte = 255;
procedure SDL_RenderDrawWuLine(renderer: PSDL_Renderer; x1, y1, x2, y2: longint); var
r, g, b, a, a_new: Uint8; gradient, iy: real; x, y: longint; px, py: plongint;
procedure swap(var a, b: longint); var tmp: longint; begin tmp := a; a := b; b := tmp; end;
begin
if a = 0 then exit; SDL_GetRenderDrawColor(renderer, @r, @g, @b, @a); if abs(y2 - y1) > abs(x2 - x1) then begin swap(x1, y1); swap(x2, y2); px := @y; py := @x; end else begin px := @x; py := @y; end; if x1 > x2 then begin swap(x1, x2); swap(y1, y2); end; x := x2 - x1; if x = 0 then x := 1; gradient := (y2 - y1) / x; iy := y1; for x := x1 to x2 do begin a_new := round(a * frac(iy)); y := floor(iy); SDL_SetRenderDrawColor(renderer, r, g, b, a-a_new); SDL_RenderDrawPoint(renderer, px^, py^); inc(y); SDL_SetRenderDrawColor(renderer, r, g, b, a_new); SDL_RenderDrawPoint(renderer, px^, py^); iy := iy + gradient; end; SDL_SetRenderDrawColor(renderer, r, g, b, a);
end;
begin
SDL_Init(SDL_INIT_VIDEO); win := SDL_CreateWindow('Xiaolin Wus line algorithm', SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 640, 480, SDL_WINDOW_RESIZABLE); ren := SDL_CreateRenderer(win, -1, 0); if ren = NIL then begin writeln(SDL_GetError); halt; end; SDL_SetRenderDrawBlendMode(ren, SDL_BLENDMODE_BLEND); SDL_RenderSetScale(ren, SCALE, SCALE); SDL_SetCursor(SDL_CreateSystemCursor(SDL_SYSTEM_CURSOR_CROSSHAIR));
mouse_x := 0; mouse_y := 0; origin.x := 0; origin.y := 0; repeat while SDL_PollEvent(@event) = 1 do case event.type_ of SDL_KEYDOWN: if event.key.keysym.sym = SDLK_ESCAPE then halt; SDL_MOUSEBUTTONDOWN: begin origin.x := mouse_x; origin.y := mouse_y; end; SDL_MOUSEMOTION: with event.motion do begin mouse_x := x div SCALE; mouse_y := y div SCALE; end; SDL_MOUSEWHEEL: line_alpha := EnsureRange(line_alpha + event.wheel.y * 20, 0, 255); SDL_QUITEV: halt; end;
SDL_SetRenderDrawColor(ren, 35, 35, 35, line_alpha); SDL_RenderDrawWuLine(ren, origin.x, origin.y, mouse_x, mouse_y); SDL_RenderPresent(ren); SDL_SetRenderDrawColor(ren, 255, 255, 255, 255); SDL_RenderClear(ren); SDL_Delay(FPS); until false;
end. </lang>
Perl
This is mostly a translation of the pseudo-code on Wikipedia, except that the $plot trick was inspired by the perl6 RosettaCode example. <lang perl>#!perl use strict; use warnings;
sub plot { my ($x, $y, $c) = @_; printf "plot %d %d %.1f\n", $x, $y, $c if $c; }
sub ipart { int shift; }
sub round { int( 0.5 + shift ); }
sub fpart { my $x = shift; $x - int $x; }
sub rfpart { 1 - fpart(shift); }
sub drawLine { my ($x0, $y0, $x1, $y1) = @_;
my $plot = \&plot;
if( abs($y1 - $y0) > abs($x1 - $x0) ) { $plot = sub { plot( @_[1, 0, 2] ) }; ($x0, $y0, $x1, $y1) = ($y0, $x0, $y1, $x1); }
if( $x0 > $x1 ) { ($x0, $x1, $y0, $y1) = ($x1, $x0, $y1, $y0); }
my $dx = $x1 - $x0; my $dy = $y1 - $y0; my $gradient = $dy / $dx;
my @xends; my $intery;
# handle the endpoints for my $xy ([$x0, $y0], [$x1, $y1]) { my ($x, $y) = @$xy; my $xend = round($x); my $yend = $y + $gradient * ($xend - $x); my $xgap = rfpart($x + 0.5);
my $x_pixel = $xend; my $y_pixel = ipart($yend); push @xends, $x_pixel;
$plot->($x_pixel, $y_pixel , rfpart($yend) * $xgap); $plot->($x_pixel, $y_pixel+1, fpart($yend) * $xgap); next if defined $intery; # first y-intersection for the main loop $intery = $yend + $gradient; }
# main loop
for my $x ( $xends[0] + 1 .. $xends[1] - 1 ) { $plot->($x, ipart ($intery), rfpart($intery)); $plot->($x, ipart ($intery)+1, fpart($intery)); $intery += $gradient; } }
if( $0 eq __FILE__ ) { drawLine( 0, 1, 10, 2 ); } __END__ </lang>
- Output:
plot 0 1 0.5 plot 10 2 0.5 plot 1 1 0.9 plot 1 2 0.1 plot 2 1 0.8 plot 2 2 0.2 plot 3 1 0.7 plot 3 2 0.3 plot 4 1 0.6 plot 4 2 0.4 plot 5 1 0.5 plot 5 2 0.5 plot 6 1 0.4 plot 6 2 0.6 plot 7 1 0.3 plot 7 2 0.7 plot 8 1 0.2 plot 8 2 0.8 plot 9 1 0.1 plot 9 2 0.9
Perl 6
<lang perl6>sub plot(\x, \y, \c) { say "plot {x} {y} {c}" }
sub fpart(\x) { x - floor(x) }
sub draw-line(@a is copy, @b is copy) {
my Bool \steep = abs(@b[1] - @a[1]) > abs(@b[0] - @a[0]); my $plot = &OUTER::plot; if steep {
$plot = -> $y, $x, $c { plot($x, $y, $c) } @a.=reverse; @b.=reverse;
} if @a[0] > @b[0] { my @t = @a; @a = @b; @b = @t }
my (\x0,\y0) = @a; my (\x1,\y1) = @b; my \dx = x1 - x0; my \dy = y1 - y0; my \gradient = dy / dx; # handle first endpoint my \x-end1 = round(x0); my \y-end1 = y0 + gradient * (x-end1 - x0); my \x-gap1 = 1 - round(x0 + 0.5);
my \x-pxl1 = x-end1; # this will be used in the main loop my \y-pxl1 = floor(y-end1); my \c1 = fpart(y-end1) * x-gap1;
$plot(x-pxl1, y-pxl1 , 1 - c1) unless c1 == 1; $plot(x-pxl1, y-pxl1 + 1, c1 ) unless c1 == 0; # handle second endpoint my \x-end2 = round(x1); my \y-end2 = y1 + gradient * (x-end2 - x1); my \x-gap2 = fpart(x1 + 0.5);
my \x-pxl2 = x-end2; # this will be used in the main loop my \y-pxl2 = floor(y-end2); my \c2 = fpart(y-end2) * x-gap2; my \intery = y-end1 + gradient;
# main loop for (x-pxl1 + 1 .. x-pxl2 - 1)
Z (intery, intery + gradient ... *)
-> \x,\y {
my \c = fpart(y); $plot(x, floor(y) , 1 - c) unless c == 1; $plot(x, floor(y) + 1, c ) unless c == 0;
}
$plot(x-pxl2, y-pxl2 , 1 - c2) unless c2 == 1; $plot(x-pxl2, y-pxl2 + 1, c2 ) unless c2 == 0;
}
draw-line [0,1], [10,2];</lang>
- Output:
plot 0 1 1 plot 1 1 0.9 plot 1 2 0.1 plot 2 1 0.8 plot 2 2 0.2 plot 3 1 0.7 plot 3 2 0.3 plot 4 1 0.6 plot 4 2 0.4 plot 5 1 0.5 plot 5 2 0.5 plot 6 1 0.4 plot 6 2 0.6 plot 7 1 0.3 plot 7 2 0.7 plot 8 1 0.2 plot 8 2 0.8 plot 9 1 0.1 plot 9 2 0.9 plot 10 2 1
PicoLisp
<lang PicoLisp>(scl 2)
(de plot (Img X Y C)
(set (nth Img (*/ Y 1.0) (*/ X 1.0)) (- 100 C)) )
(de ipart (X)
(* 1.0 (/ X 1.0)) )
(de iround (X)
(ipart (+ X 0.5)) )
(de fpart (X)
(% X 1.0) )
(de rfpart (X)
(- 1.0 (fpart X)) )
(de xiaolin (Img X1 Y1 X2 Y2)
(let (DX (- X2 X1) DY (- Y2 Y1)) (use (Grad Xend Yend Xgap Xpxl1 Ypxl1 Xpxl2 Ypxl2 Intery) (when (> (abs DY) (abs DX)) (xchg 'X1 'Y1 'X2 'Y2) ) (when (> X1 X2) (xchg 'X1 'X2 'Y1 'Y2) ) (setq Grad (*/ DY 1.0 DX) Xend (iround X1) Yend (+ Y1 (*/ Grad (- Xend X1) 1.0)) Xgap (rfpart (+ X1 0.5)) Xpxl1 Xend Ypxl1 (ipart Yend) ) (plot Img Xpxl1 Ypxl1 (*/ (rfpart Yend) Xgap 1.0)) (plot Img Xpxl1 (+ 1.0 Ypxl1) (*/ (fpart Yend) Xgap 1.0)) (setq Intery (+ Yend Grad) Xend (iround X2) Yend (+ Y2 (*/ Grad (- Xend X2) 1.0)) Xgap (fpart (+ X2 0.5)) Xpxl2 Xend Ypxl2 (ipart Yend) ) (plot Img Xpxl2 Ypxl2 (*/ (rfpart Yend) Xgap 1.0)) (plot Img Xpxl2 (+ 1.0 Ypxl2) (*/ (fpart Yend) Xgap 1.0)) (for (X (+ Xpxl1 1.0) (>= (- Xpxl2 1.0) X) (+ X 1.0)) (plot Img X (ipart Intery) (rfpart Intery)) (plot Img X (+ 1.0 (ipart Intery)) (fpart Intery)) (inc 'Intery Grad) ) ) ) )
(let Img (make (do 90 (link (need 120 99)))) # Create image 120 x 90
(xiaolin Img 10.0 10.0 110.0 80.0) # Draw lines (xiaolin Img 10.0 10.0 110.0 45.0) (xiaolin Img 10.0 80.0 110.0 45.0) (xiaolin Img 10.0 80.0 110.0 10.0) (out "img.pgm" # Write to bitmap file (prinl "P2") (prinl 120 " " 90) (prinl 100) (for Y Img (apply printsp Y)) ) )</lang>
PureBasic
<lang PureBasic>Macro PlotB(x, y, Color, b)
Plot(x, y, RGB(Red(Color) * (b), Green(Color) * (b), Blue(Color) * (b)))
EndMacro
Procedure.f fracPart(x.f)
ProcedureReturn x - Int(x)
EndProcedure
Procedure.f invFracPart(x.f)
ProcedureReturn 1.0 - fracPart(x)
EndProcedure
Procedure drawAntiAliasedLine(x1.f, y1.f, x2.f, y2.f, color)
Protected.f dx, dy, xend, yend, grad, yf, xgap, ix1, iy1, ix2, iy2 Protected x dx = x2 - x1 dy = y2 - y1 If Abs(dx) < Abs(dy) Swap x1, y1 Swap x2, y2 Swap dx, dy EndIf If x2 < x1 Swap x1, x2 Swap y1, y2 EndIf grad = dy / dx ;handle first endpoint xend = Round(x1, #pb_round_nearest) yend = y1 + grad * (xend - x1) xgap = invFracPart(x1 + 0.5) ix1 = xend ;this will be used in the MAIN loop iy1 = Int(yend) PlotB(ix1, iy1, color, invFracPart(yend) * xgap) PlotB(ix1, iy1 + 1, color, fracPart(yend) * xgap) yf = yend + grad ;first y-intersection for the MAIN loop ;handle second endpoint xend = Round(x2, #pb_round_nearest) yend = y2 + grad * (xend - x2) xgap = fracPart(x2 + 0.5) ix2 = xend ;this will be used in the MAIN loop iy2 = Int(yend) PlotB(ix2, iy2, color, invFracPart(yend) * xgap) PlotB(ix2, iy2 + 1, color, fracPart(yend) * xgap) ;MAIN loop For x = ix1 + 1 To ix2 - 1 PlotB(x, Int(yf), color, invFracPart(yf)) PlotB(x, Int(yf) + 1, color, fracPart(yf)) yf + grad Next
EndProcedure
Define w = 200, h = 200, img = 1 CreateImage(img, w, h) ;img is internal id of the image
OpenWindow(0, 0, 0, w, h,"Xiaolin Wu's line algorithm", #PB_Window_SystemMenu)
StartDrawing(ImageOutput(img))
drawAntiAliasedLine(80,20, 130,80, RGB(255, 0, 0))
StopDrawing()
ImageGadget(0, 0, 0, w, h, ImageID(img))
Define event Repeat
event = WaitWindowEvent()
Until event = #PB_Event_CloseWindow</lang>
Python
<lang python>"""Script demonstrating drawing of anti-aliased lines using Xiaolin Wu's line algorithm
usage: python xiaolinwu.py [output-file]
""" from __future__ import division import sys
from PIL import Image
def _fpart(x):
return x - int(x)
def _rfpart(x):
return 1 - _fpart(x)
def putpixel(img, xy, color, alpha=1):
"""Paints color over the background at the point xy in img. Use alpha for blending. alpha=1 means a completely opaque foreground.
""" c = tuple(map(lambda bg, fg: int(round(alpha * fg + (1-alpha) * bg)), img.getpixel(xy), color)) img.putpixel(xy, c)
def draw_line(img, p1, p2, color):
"""Draws an anti-aliased line in img from p1 to p2 with the given color.""" x1, y1, x2, y2 = p1 + p2 dx, dy = x2-x1, y2-y1 steep = abs(dx) < abs(dy) p = lambda px, py: ((px,py), (py,px))[steep]
if steep: x1, y1, x2, y2, dx, dy = y1, x1, y2, x2, dy, dx if x2 < x1: x1, x2, y1, y2 = x2, x1, y2, y1
grad = dy/dx intery = y1 + _rfpart(x1) * grad def draw_endpoint(pt): x, y = pt xend = round(x) yend = y + grad * (xend - x) xgap = _rfpart(x + 0.5) px, py = int(xend), int(yend) putpixel(img, (px, py), color, _rfpart(yend) * xgap) putpixel(img, (px, py+1), color, _fpart(yend) * xgap) return px
xstart = draw_endpoint(p(*p1)) + 1 xend = draw_endpoint(p(*p2))
for x in range(xstart, xend): y = int(intery) putpixel(img, p(x, y), color, _rfpart(intery)) putpixel(img, p(x, y+1), color, _fpart(intery)) intery += grad
if __name__ == '__main__':
if len(sys.argv) != 2: print 'usage: python xiaolinwu.py [output-file]' sys.exit(-1)
blue = (0, 0, 255) yellow = (255, 255, 0) img = Image.new("RGB", (500,500), blue) for a in range(10, 431, 60): draw_line(img, (10, 10), (490, a), yellow) draw_line(img, (10, 10), (a, 490), yellow) draw_line(img, (10, 10), (490, 490), yellow) filename = sys.argv[1] img.save(filename) print 'image saved to', filename</lang>
Racket
<lang racket>#lang racket (require 2htdp/image)
(define (plot img x y c)
(define c*255 (exact-round (* (- 1 c) 255))) (place-image (rectangle 1 1 'solid (make-color c*255 c*255 c*255 255)) x y img))
(define ipart exact-floor) ; assume that a "round-down" is what we want when -ve
- `round` is built in -- but we'll use exact round (and I'm not keen on over-binding round)
(define (fpart n) (- n (exact-floor n))) (define (rfpart n) (- 1 (fpart n)))
(define (draw-line img x0 y0 x1 y1)
(define (draw-line-steeped img x0 y0 x1 y1 steep?) (define (draw-line-steeped-l-to-r img x0 y0 x1 y1 steep?) (define dx (- x1 x0)) (define dy (- y1 y0)) (define gradient (/ dy dx)) (define (handle-end-point img x y) (define xend (exact-round x)) (define yend (+ y (* gradient (- xend x)))) (define xgap (rfpart (+ x 0.5))) (define ypxl (ipart yend)) (define intery (+ yend gradient)) (case steep? [(#t) (define img* (plot img ypxl xend (* xgap (rfpart yend)))) (values (plot img* (+ ypxl 1) xend (* xgap (fpart yend))) xend intery)] [(#f) (define img* (plot img xend ypxl (* xgap (rfpart yend)))) (values (plot img* xend (+ ypxl 1) (* xgap (fpart yend))) xend intery)])) (define-values (img-with-l-endpoint xpl1 intery) (handle-end-point img x0 y0)) (define-values (img-with-r-endpoint xpl2 _) (handle-end-point img-with-l-endpoint x1 y1)) (for/fold ((img img-with-l-endpoint) (y intery)) ((x (in-range (+ xpl1 1) xpl2))) (define y-i (ipart y)) (values (case steep? [(#t) (define img* (plot img y-i x (rfpart y))) (plot img* (+ 1 y-i) x (fpart y))] [(#f) (define img* (plot img x y-i (rfpart y))) (plot img* x (+ 1 y-i) (fpart y))]) (+ y gradient)))) (if (> x0 x1) (draw-line-steeped-l-to-r img x1 y1 x0 y0 steep?) (draw-line-steeped-l-to-r img x0 y0 x1 y1 steep?))) (define steep? (> (abs (- y1 y0)) (abs (- x1 x0)))) (define-values (img* _) (if steep? (draw-line-steeped img y0 x0 y1 x1 steep?) (draw-line-steeped img x0 y0 x1 y1 steep?))) img*)
(define img-1 (beside
(scale 3 (draw-line (empty-scene 150 100) 12 12 138 88)) (above (scale 1 (draw-line (empty-scene 150 100) 12 50 138 50)) (scale 1 (draw-line (empty-scene 150 100) 75 12 75 88)) (scale 1 (draw-line (empty-scene 150 100) 12 88 138 12)))))
(define img-2
(beside (scale 3 (draw-line (empty-scene 100 150) 12 12 88 138)) (above (scale 1 (draw-line (empty-scene 100 150) 50 12 50 138)) (scale 1 (draw-line (empty-scene 100 150) 12 75 88 75)) (scale 1 (draw-line (empty-scene 100 150) 88 12 12 138)))))
img-1 img-2 (save-image img-1 "images/xiaolin-wu-racket-1.png") (save-image img-2 "images/xiaolin-wu-racket-2.png")</lang>
Output files: File:Xiaolin-wu-racket-1.png File:Xiaolin-wu-racket-2.png
REXX
This REXX example uses the Xiaolin Wu line algorithm to draw a line (with output).
Apparently, there may be an error in the definition of the algorithm (which only manifests itself with negative numbers):
use of the IPART function should probably be FLOOR.
[See the talk section on the Xiaolin Wu's line algorithm.]
http://en.wikipedia.org/wiki/Talk:Xiaolin_Wu%27s_line_algorithm
Also, it takes in account (that can easily be overlooked) of the note after the description of the algorithm:
Note: If at the beginning of the routine abs(dx) < abs(dy) is true, then all plotting should be done with x and y reversed.
<lang rexx>/*REXX program plots/draws a line using the Xiaolin Wu line algorithm.*/
background = 'fa'x /*background char: middle-dot. */
image. = background /*fill the array with middle-dots*/ plotC = '░▒▓█' /*chars used for plotting points.*/ EoE = 1000 /*EOE = End Of Earth, er... plot.*/ do j=-EoE to +EoE /*draw grid from lowest──►highest*/ image.j.0 = '─' /*draw the horizontal axis. */ image.0.j = '│' /* " " verical " */ end /*j*/
image.0.0 = '┼' /*"draw" the axis origin (char). */ parse arg xi yi xf yf . /*allow specifying line-end pts. */ if xi== | xi==',' then xi = 1 /*if not specified, use default. */ if yi== | yi==',' then yi = 2 /* " " " " " */ if xf== | xf==',' then xf = 11 /* " " " " " */ if yf== | yf==',' then yf = 12 /* " " " " " */ minX=0; minY=0 /*used as limits for plotting. */ maxX=0; maxY=0 /* " " " " " */ call line_draw xi, yi, xf, yf /*call subroutine and draw line. */ border = 2 /*allow additional space for plot*/ minX=minX-border*2; maxX=maxX+border*2 minY=minY-border ; maxY=maxY+border
do y=maxY by -1 to minY; _= /*build a row*/ do x=minX to maxX _=_ || image.x.y end /*x*/ say _ /*display row*/ end /*y*/
exit /*stick a fork in it, we're done.*/ /*────────────────────────────────DRAW_LINE subroutine──────────────────*/ line_draw: procedure expose background image. minX maxX minY maxY plotC parse arg x1, y1, x2, y2; switchXY=0; dx=x2-x1
dy=y2-y1
if abs(dx)<abs(dy) then do
parse value x1 y1 with y1 x1 /*swap x1 & y1*/ parse value x2 y2 with y2 x2 /*swap x2 & y2*/ parse value dx dy with dy dx /*swap dx & dy*/ end
if x2<x1 then do
parse value x1 x2 with x2 x1 /*swap x1 & x2*/ parse value y1 y2 with y2 y1 /*swap y1 & y2*/ switchXY=1 end
gradient = dy/dx
xend = round(x1) /*────1st endpoint────────────────────*/ yend = y1 + gradient * (xend-x1) intery = yend + gradient xgap = 1 - fpart(x1+.5) xpx11 = xend; ypx11 = floor(yend); ypx11_=ypx11+1
call plotXY xpx11, ypx11, brite(1-fpart(yend*xgap)),switchXY call plotXY xpx11, ypx11_, brite( fpart(yend*xgap)),switchXY
xend = round(x2) /*────2nd endpoint────────────────────*/ yend = y2 + gradient * (xend-x2) xgap = fpart(x2+.5) xpx12 = xend; ypx12 = floor(yend); ypx12_=ypx12+1
call plotXY xpx12, ypx12, brite(1-fpart(yend*xgap)), switchXY call plotXY xpx12, ypx12_, brite( fpart(yend*xgap)), switchXY
do x=xpx11+1 to xpx12-1 /*────draw the line───────────────────*/ !intery = floor(intery) !intery_ = !intery+1 call plotXY x, !intery, brite(1-fpart(intery)), switchXY call plotXY x, !intery_, brite( fpart(intery)), switchXY intery = intery + gradient end /*x*/
return /*────────────────────────────────BRITE subroutine──────────────────────*/ brite: procedure expose background plotC; parse arg p return substr(background || plotC, 1+round(abs(p)*length(plotC)), 1) /*────────────────────────────────PLOTXY subroutine─────────────────────*/ plotXY: procedure expose image. minX maxX minY maxY parse arg xx, yy, bc, switchYX; if switchYX then parse arg yy, xx image.xx.yy=bc; minX=min(minX,xx); maxX=max(maxX,xx)
minY=min(minY,yy); maxY=max(maxY,yy)
return /*────────────────────────────────FLOOR subroutine──────────────────────*/ floor: procedure; parse arg ?; _=trunc(?); return _-(?<0)*(?\=_) /*────────────────────────────────FPART subroutine──────────────────────*/ fpart: procedure; parse arg ?; return abs(?-trunc(?)) /*────────────────────────────────ROUND subroutine─────────arg2 is place*/ round: return format(arg(1), , word(arg(2) 0, 1))</lang> output when using the default input
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Ruby
<lang ruby>def ipart(n); n.truncate; end def fpart(n); n - ipart(n); end def rfpart(n); 1.0 - fpart(n); end
class Pixmap
def draw_line_antialised(p1, p2, colour) x1, y1 = p1.x, p1.y x2, y2 = p2.x, p2.y steep = (y2 - y1).abs > (x2 - x1).abs if steep x1, y1 = y1, x1 x2, y2 = y2, x2 end if x1 > x2 x1, x2 = x2, x1 y1, y2 = y2, y1 end deltax = x2 - x1 deltay = (y2 - y1).abs gradient = 1.0 * deltay / deltax # handle the first endpoint xend = x1.round yend = y1 + gradient * (xend - x1) xgap = rfpart(x1 + 0.5) xpxl1 = xend ypxl1 = ipart(yend) put_colour(xpxl1, ypxl1, colour, steep, rfpart(yend)*xgap) put_colour(xpxl1, ypxl1 + 1, colour, steep, fpart(yend)*xgap) itery = yend + gradient # handle the second endpoint xend = x2.round yend = y2 + gradient * (xend - x2) xgap = rfpart(x2 + 0.5) xpxl2 = xend ypxl2 = ipart(yend) put_colour(xpxl2, ypxl2, colour, steep, rfpart(yend)*xgap) put_colour(xpxl2, ypxl2 + 1, colour, steep, fpart(yend)*xgap) # in between (xpxl1 + 1).upto(xpxl2 - 1).each do |x| put_colour(x, ipart(itery), colour, steep, rfpart(itery)) put_colour(x, ipart(itery) + 1, colour, steep, fpart(itery)) itery = itery + gradient end end
def put_colour(x, y, colour, steep, c) x, y = y, x if steep self[x, y] = anti_alias(colour, self[x, y], c) end
def anti_alias(new, old, ratio) blended = new.values.zip(old.values).map {|n, o| (n*ratio + o*(1.0 - ratio)).round} RGBColour.new(*blended) end
end
bitmap = Pixmap.new(500, 500) bitmap.fill(RGBColour::BLUE) 10.step(430, 60) do |a|
bitmap.draw_line_antialised(Pixel[10, 10], Pixel[490,a], RGBColour::YELLOW) bitmap.draw_line_antialised(Pixel[10, 10], Pixel[a,490], RGBColour::YELLOW)
end bitmap.draw_line_antialised(Pixel[10, 10], Pixel[490,490], RGBColour::YELLOW)</lang>
Tcl
Uses code from Basic bitmap storage#Tcl <lang tcl>package require Tcl 8.5 package require Tk
proc ::tcl::mathfunc::ipart x {expr {int($x)}} proc ::tcl::mathfunc::fpart x {expr {$x - int($x)}} proc ::tcl::mathfunc::rfpart x {expr {1.0 - fpart($x)}}
proc drawAntialiasedLine {image colour p1 p2} {
lassign $p1 x1 y1 lassign $p2 x2 y2
set steep [expr {abs($y2 - $y1) > abs($x2 - $x1)}] if {$steep} { lassign [list $x1 $y1] y1 x1 lassign [list $x2 $y2] y2 x2 } if {$x1 > $x2} { lassign [list $x1 $x2] x2 x1 lassign [list $y1 $y2] y2 y1 } set deltax [expr {$x2 - $x1}] set deltay [expr {abs($y2 - $y1)}] set gradient [expr {1.0 * $deltay / $deltax}] # handle the first endpoint set xend [expr {round($x1)}] set yend [expr {$y1 + $gradient * ($xend - $x1)}] set xgap [expr {rfpart($x1 + 0.5)}] set xpxl1 $xend set ypxl1 [expr {ipart($yend)}] plot $image $colour $steep $xpxl1 $ypxl1 [expr {rfpart($yend)*$xgap}] plot $image $colour $steep $xpxl1 [expr {$ypxl1+1}] [expr {fpart($yend)*$xgap}] set itery [expr {$yend + $gradient}]
# handle the second endpoint set xend [expr {round($x2)}] set yend [expr {$y2 + $gradient * ($xend - $x2)}] set xgap [expr {rfpart($x2 + 0.5)}] set xpxl2 $xend set ypxl2 [expr {ipart($yend)}] plot $image $colour $steep $xpxl2 $ypxl2 [expr {rfpart($yend)*$xgap}] plot $image $colour $steep $xpxl2 [expr {$ypxl2+1}] [expr {fpart($yend)*$xgap}]
for {set x [expr {$xpxl1 + 1}]} {$x < $xpxl2} {incr x} { plot $image $colour $steep $x [expr {ipart($itery)}] [expr {rfpart($itery)}] plot $image $colour $steep $x [expr {ipart($itery) + 1}] [expr {fpart($itery)}] set itery [expr {$itery + $gradient}] }
}
proc plot {image colour steep x y c} {
set point [expr {$steep ? [list $y $x] : [list $x $y]}] set newColour [antialias $colour [getPixel $image $point] $c] setPixel $image $newColour $point
}
proc antialias {newColour oldColour c} {
# get the new colour r,g,b if {[scan $newColour "#%2x%2x%2x%c" nr ng gb -] != 3} { scan [colour2rgb $newColour] "#%2x%2x%2x" nr ng nb }
# get the current colour r,g,b scan $oldColour "#%2x%2x%2x" cr cg cb # blend the colours in the ratio defined by "c" foreach new [list $nr $ng $nb] curr [list $cr $cg $cb] { append blend [format {%02x} [expr {round($new*$c + $curr*(1.0-$c))}]] } return #$blend
}
proc colour2rgb {color_name} {
foreach part [winfo rgb . $color_name] { append colour [format %02x [expr {$part >> 8}]] } return #$colour
}
set img [newImage 500 500] fill $img blue for {set a 10} {$a < 500} {incr a 60} {
drawAntialiasedLine $img yellow {10 10} [list 490 $a] drawAntialiasedLine $img yellow {10 10} [list $a 490]
} toplevel .wu label .wu.l -image $img pack .wu.l</lang>