如何在中心绘制一个带有alpha方形的正方形

Question

我知道如何画一个正方形:

graphics.moveTo(0, 0);
graphics.beginFill(0x00ff00, 1);
graphics.lineTo(point, 0);
graphics.lineTo(point, point);
graphics.lineTo(0, point);
graphics.lineTo(0, 0);
graphics.endFill();

现在,我将如何在第一个方格内绘制另一个方形,其中alpha为0.5？

Answer 1

下面的代码片段将绘制一个绿色方块,然后将一个方块减去其中心(现场演示).

// Size of the main square
var point:uint = 100;

// Create two sprites
var s1:Sprite = new Sprite();
var s2:Sprite = new Sprite();

// Shortcuts to graphics objects
var g1:Graphics = s1.graphics;
var g2:Graphics = s2.graphics;

// Draw the main square
g1.beginFill(0x00ff00, 1.0);
g1.drawRect(0, 0, point, point);
g1.endFill();

// Draw the eraser square 
g2.beginFill(0x000000, 0.5);
g2.drawRect(0, 0, point/2, point/2);
g2.endFill();

// Configure blend modes to erase the center of the first square
s1.blendMode = BlendMode.LAYER;
s2.blendMode = BlendMode.ERASE;

// Add the eraser square to the first one and adjust its position
s1.addChild(s2);
s2.x = s2.y = point/4;

// Add the first square to the stage
addChild(s1);