我onDraw通过自定义视图的方法在 画布上设置矩阵,canvas.setMatrix(matrix);然后使用预定义的绘画绘制网格:
onDraw
canvas.setMatrix(matrix);
canvas.drawRect(0,0,viewWidth,viewHeight, background); for(int i=0; i <= nRows; i++){ canvas.drawLine(0,i*cellHeight, nCols*cellWidth,i*cellHeight,lines); canvas.drawLine(i*cellWidth, 0, i*cellWidth, nRows*cellHeight, lines); if(i != nRows) canvas.drawText(""+i, i*cellWidth, (i+1)*cellHeight, text); }
由于某种原因,整个画布的偏移量约为单元格高度的1.5倍。知道为什么会这样或如何解决吗?矩阵尚未初始化,因此根据文档应该是标识。
非常感谢!
我已经收窄这种行为降低到原来的Matrix一个的View的帆布已经被视图的位置转换。但是,如果您Matrix使用Canvas.getMatrix()或,则这并不明显View.getMatrix()。您将从这些调用中获得身份矩阵。
Matrix
View
Canvas.getMatrix()
View.getMatrix()
您看到的画布偏移很可能View与屏幕顶部(状态栏,标题栏等)的偏移高度完全相同。
在大多数情况下,您可以使用canvas.concat(matrix)代替canvas.setMatrix(matrix)此用例,这是正确的。如果您确实需要原始矩阵(我在调试时做了),则必须通过View自身的翻译手动对其进行转换Window:
canvas.concat(matrix)
canvas.setMatrix(matrix)
Window
int[] viewLocation = new int[2]; mView.getLocationInWindow(viewLocation); mOriginalMatrix.setTranslate(viewLocation[0], viewLocation[1]);
编辑 以回答评论中的其他问题:
要转换触摸坐标(或任何屏幕坐标)以匹配a的坐标Canvas,只需将所有转换改为a Matrix,并Canvas.concat()在绘制之前每帧使用该矩阵。(或者您可以Canvas像现在一样直接进行所有转换,并Canvas.getMatrix(mMyMatrix)在每次绘制后使用来检索矩阵。不建议使用,但是可以使用。)
Canvas
Canvas.concat()
Canvas.getMatrix(mMyMatrix)
然后可以使用矩阵将原始网格边界转换为在屏幕上绘制的边界。本质上,您所做的与Canvas绘制网格时完全相同,将网格的角点转换为屏幕坐标。现在,网格将与触摸事件位于同一坐标系中:
private final Matrix mMyMatrix = new Matrix(); // Assumes that the grid covers the whole View. private final float[] mOriginalGridCorners = new float[] { 0, 0, // top left (x, y) getWidth(), getHeight() // bottom right (x, y) }; private final float[] mTransformedGridCorners = new float[4]; @Override public boolean onTouchEvent(MotionEvent event) { if (/* User pans the screen */) { mMyMatrix.postTranslate(deltaX, deltaY); } if (/* User zooms the screen */) { mMyMatrix.postScale(deltaScale, deltaScale); } if (/* User taps the grid */) { // Transform the original grid corners to where they // are on the screen (panned and zoomed). mMyMatrix.mapPoints(mTransformedGridCorners, mOriginalGridCorners); float gridWidth = mTransformedGridCorners[2] - mTransformedGridCorners[0]; float gridHeight = mTransformedGridCorners[3] - mTransformedGridCorners[1]; // Get the x and y coordinate of the tap inside the // grid, between 0 and 1. float x = (event.getX() - mTransformedGridCorners[0]) / gridWidth; float y = (event.getY() - mTransformedGridCorners[1]) / gridHeight; // To get the tapped grid cell. int column = (int)(x * nbrColumns); int row = (int)(y * nbrRows); // Or to get the tapped exact pixel in the original grid. int pixelX = (int)(x * getWidth()); int pixelY = (int)(y * getHeight()); } return true; } @Override protected void onDraw(Canvas canvas) { // Each frame, transform your canvas with the matrix. canvas.save(); canvas.concat(mMyMatrix); // Draw grid. grid.draw(canvas); canvas.restore(); }
或者不推荐使用的方法来获取矩阵,该方法仍然有效,并且可能需要较少的更改:
@Override protected void onDraw(Canvas canvas) { canvas.save(); // Transform canvas and draw the grid. grid.draw(canvas); // Get the matrix from canvas. Can be used to transform // corners on the next touch event. canvas.getMatrix(mMyMatrix); canvas.restore(); }