Just another update

Task/Xiaolin-Wus-line-algorithm/Pascal/xiaolin-wus-line-algorithm.pascal

@@ -0,0 +1,122 @@
+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 Wu''s 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.