畫線的算法不少，但要作到高速、簡單并不輕易。斜率相乘法是最簡單的方法之一，但計算每個點均要花費不少時間用于乘、除法運算；下面介紹的是Bresenham's高效畫線算法，對每個點的坐標計算只要加、減法就能完成。 簡化算法用偽Pascal語言描述如下： PRocedure DrawLine(x1, y1, x2, y2: Integer); var x, y, DeltaX, DeltaY, HalfX, ErrorTerm, i: Integer; begin DeltaX := x2 - x1; DeltaY := y2 - y1; HalfX := (x2 - x1) shr 1; ErrorTerm := 0; x := x1; y := y1; for i:=0 to DeltaX do begin Plot(X, Y); Inc(x); ErrorTerm := ErrorTerm + DeltaY; if ErrorTerm>HalfX then begin ErrorTerm := ErrorTerm - DeltaX; Inc(y); end; end; end; 為方便閱讀，上述程序作了簡化。實際程序應略作修正，以分別處理DeltaX與DeltaY比較大小, 必要時交換起始、結束點等。 修正后的的偽Pascal算法如下： procedure DrawLine(x1, y1, x2, y2: Integer); var x, y, DeltaX, DeltaY, HalfCount, ErrorTerm, i, Flag: Integer; begin DeltaX := x2 - x1; DeltaY := y2 - y1; if Abs(DeltaY)<Abs(DeltaX) then begin if DeltaX<0 then begin i := x1; x1 := x2; x2 := i; i := y1; y1 := y2; y2 := i; DeltaX := x2 - x1; DeltaY := y2 - y1; end; if DeltaY<0 then Flag := -1 else Flag := 1; DeltaY := Abs(DeltaY); HalfCount := DeltaX shr 1; ErrorTerm := 0; x := x1; y := y1; for i:=0 to DeltaX do begin Plot(X, Y); Inc(x); ErrorTerm := ErrorTerm + DeltaY; if ErrorTerm>HalfCount then begin ErrorTerm := ErrorTerm - DeltaX; y := y + Flag; end; end; end else begin if DeltaY<0 then begin i := x1; x1 := x2; x2 := i; i := y1; y1 := y2; y2 := i; DeltaX := x2 - x1; DeltaY := y2 - y1; end; if DeltaX<0 then Flag := -1 else Flag := 1; DeltaX := Abs(DeltaX); HalfCount := DeltaY shr 1; ErrorTerm := 0; x := x1; y := y1; for i:=0 to DeltaY do begin Plot(X, Y); Inc(y); ErrorTerm := ErrorTerm + DeltaX; if ErrorTerm>HalfCount then begin ErrorTerm := ErrorTerm - DeltaY; x := x + Flag; end; end; end; end;
