BGRABitmap tutorial 14
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This tutorial show how to use Canvas2D property of BGRABitmap. Canvas2D is designed to work as the javascript 2d context of the HTML Canvas object.
First program
Here is a very simple example : <delphi> procedure TForm1.FormPaint(Sender: TObject); var bmp: TBGRABitmap;
ctx: TBGRACanvas2D;
begin
bmp := TBGRABitmap.Create(ClientWidth,ClientHeight,BGRA(210,210,210));
ctx := bmp.Canvas2D;
ctx.fillStyle('rgb(240,128,0)');
ctx.fillRect(30,30,80,60);
ctx.strokeRect(50,50,80,60);
bmp.Draw(Canvas,0,0); bmp.Free;
end; </delphi>
The bitmap has a Canvas2D property which provides the fillRect and strokeRect function. The fillStyle is defined to orange by specifying a css color string. When the shape is filled, it uses the fill style, and when the border is drawn, it uses the stroke style.
The code above is equivalent to this javascript code : <javascript>
var canvas = document.getElementsByTagName("canvas")[0];
canvas.width = 200
canvas.height = 200
if (canvas.getContext){
var ctx = canvas.getContext("2d");
ctx.fillStyle = "rgb(240,128,0)";
ctx.fillRect(30,30,80,60);
ctx.strokeRect(50,50,80,60);
}
</javascript>
Complex shapes
To draw a complex shape, it is necessary to define a path : <delphi> procedure pave();
begin
ctx.fillStyle ('rgb(130,100,255)');
ctx.strokeStyle ('rgb(0,0,255)');
ctx.beginPath();
ctx.lineWidth:=2;
ctx.moveTo(5,5);ctx.lineTo(20,10);ctx.lineTo(55,5);ctx.lineTo(45,18);ctx.lineTo(30,50);
ctx.closePath();
ctx.stroke();
ctx.fill();
end;
begin
bmp := TBGRABitmap.Create(ClientWidth,ClientHeight,BGRA(210,210,210)); ctx := bmp.Canvas2D; pave(); bmp.Draw(Canvas,0,0); bmp.Free;
end; </delphi>
Notice that the line width is defined by the property lineWidth and that the path begins with a beginPath call. If you want more information on the way path works, see javascript documentation.
Using transformations
Now we can draw the triangle six times with a rotation by calling transformation functions.
<delphi> procedure six();
var
i: Integer;
begin
ctx.save();
for i := 0 to 5 do
begin
ctx.rotate(2*PI/6);
pave();
end;
ctx.restore();
end;
begin
bmp := TBGRABitmap.Create(ClientWidth,ClientHeight,BGRA(210,210,210)); ctx := bmp.Canvas2D; ctx.translate(80,80); six; bmp.Draw(Canvas,0,0); bmp.Free;
end; </delphi>
More examples
Other examples are in testcanvas2d directory of BGRABitmap archive. Scripts are taken from Jean-Paul Davalan web site which contains HTML Canvas examples.
