如何实现Matrix2D图形在画布中心点放大并旋转角度

问题现象
如何在画布中心点实现Matrix2D图形指定倍数的放大和指定角度的旋转？

背景知识
Matrix2D组件的方法rotate，能够以旋转点为中心、对当前矩阵进行右乘旋转运算，调用公式为：rotate(degree: number, rx?: number, ry?: number)，其中degree为旋转角度，rx和ry为旋转中心点相对[0,0]点的水平和垂直方向坐标，如果[0,0]点通过translate发生移动，则以新的点计算相对的rx和ry值。
translate方法能够对当前矩阵进行左乘平移运算，调用公式为：translate(tx?: number, ty?: number)。
scale方法能够对当前矩阵进行右乘缩放运算，调用公式为：scale(sx?: number, sy?: number)，其中sx和sy为水平和垂直缩放比例系数。以[0,0]为基准进行缩放，如果[0,0]点通过translate发生移动，则以移动后的点为基准点进行缩放。
解决方案
使用Flex布局将Canvas组件居中显示，创建矩形。
使用rotate方法对矩阵进行旋转操作，旋转角度由angle决定，旋转中心为矩形的中心；使用scale方法对矩阵进行缩放操作，缩放倍数由scaleTimesX和scaleTimesY决定，以中心点为基准进行缩放。rotate和scale存在调用顺序，遵循就近原则，因此需要将scale方法的使用放在rotate上方。
使用translate方法对矩阵进行平移操作，将画布的原点移动到画布的中心，即可将图形移动至画布中心。将经过变换的矩阵应用到CanvasRenderingContext2D对象上。
用fillRect()方法在画布上绘制矩形。
完整示例参考如下：
@Entry
@Component
struct MatrixChange {
private settings: RenderingContextSettings = new RenderingContextSettings(true);
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings);
private matrix: Matrix2D = new Matrix2D();
x: number = 50; // 图形大小
y: number = 50; // 图形大小
canvasWidth: number = 200; // 画布大小
canvasHeight: number = 200; // 画布大小
scaleTimesX: number = 2; // 缩放设置
scaleTimesY: number = 2; // 缩放设置
angle: number = -30; // 旋转角度

build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width(this.canvasWidth)
.height(this.canvasHeight)
.backgroundColor('#0D5AF5')
.onReady(() => {
this.matrix.scaleX = 1;
this.matrix.scaleY = 1;
this.matrix.scale(this.scaleTimesX, this.scaleTimesY);
this.matrix.rotate(this.angle Math.PI / 180, this.x / 2, this.y / 2);
this.matrix.translate(this.canvasWidth / 2, this.canvasHeight / 2);
this.matrix.translate(-this.x this.scaleTimesX / 2, -this.y * this.scaleTimesY / 2);
this.context.setTransform(this.matrix);
this.context.fillRect(0, 0, this.x, this.y);
});
}
.width('100%')
.height('100%');
}
}
总结
Matrix2D图形能够在画布中心点放大指定倍数并旋转指定角度，该功能适用于需要展示图形并对其进行各种变换的场景，例如数据可视化、图形编辑器等。
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