如何找到在画布当前的翻译位置？ [英] How to find the current translate position in Canvas?

问题描述

我如何获取当前翻译从画布的位置？我想画的东西在我的坐标是相对的混合（彼此）和绝对（帆布）。

How do I get the current translate position from a Canvas? I am trying to draw stuff where my coordinates are a mix of relative (to each other) and absolute (to canvas).

可以说，我想做的事情

canvas.translate(x1, y1);
canvas.drawSomething(0, 0); // will show up at (x1, y1), all good
// now i want to draw a point at x2,y2
canvas.translate(x2, y2);
canvas.drawSomething(0, 0); // will show up at (x1+x2, y1+y2)
// i could do
canvas.drawSomething(-x1, -y1);
// but i don't always know those coords

这工作，但脏了：

private static Point getCurrentTranslate(Canvas canvas) {
    float [] pos = new float [2];
    canvas.getMatrix().mapPoints(pos);
    return new Point((int)pos[0], (int)pos[1]);
}
...
Point p = getCurrentTranslate(canvas);
canvas.drawSomething(-p.x, -p.y);

画布有getMatrix方法，它有一个 setTranslate ，但没有 getTranslate 。我不想使用 canvas.save（）和 canvas.restore（），因为我的方式绘制的东西它是一个有点棘手（也可能是凌乱...）

The canvas has a getMatrix method, it has a setTranslate but no getTranslate. I don't want to use canvas.save() and canvas.restore() because the way I'm drawing things it's a little tricky (and probably messy ...)

有一个更清洁的方式来获得这些当前坐标？

Is there a cleaner way to get these current coordinates?

推荐答案

您需要先重新设置变换矩阵。我不是一个Android开发者，看着 Android的画布文档，没有复位矩阵，但有一个setMatrix（android.graphics.Matrix）。它说，如果给定矩阵是空它将设置当前矩阵为单位矩阵，这是你想要的。所以我觉得你可以重置您的位置（和比例和倾斜）：

You need to reset the transformation matrix first. I'm not an android developer, looking at the android canvas docs, there is no reset matrix, but there is a setMatrix(android.graphics.Matrix). It says if the given matrix is null it will set the current matrix to the identity matrix, which is what you want. So I think you can reset your position (and scale and skew) with:

canvas.setMatrix(null);

也将是可能的，通过getMatrix来得到当前翻译。有一个mapVectors（）方法，你可以使用矩阵，看看点[0,0]将被映射成，这将是您的翻译。但是，在你的情况我想重置矩阵是最好的。

It would also be possible to get the current translation through getMatrix. There is a mapVectors() method you could use for matrices to see where the point [0,0] would be mapped to, this would be your translation. But in your case I think resetting the matrix is best.

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