Android图形变换矩阵
对于图像的图形变换，Android通过矩阵来进行处理，每个像素点表达了其坐标的X,Y信息。Android的图形变换矩阵是一个3*3的矩阵。
图形变换矩阵
- 平移变换
平移变换
- 旋转变换
旋转变换
如果以任意点O为旋转中心来进行旋转变换。
-
将坐标原点平移到O点
-
以坐标原点为中心进行旋转变换
-
将坐标原点还原
- 缩放变换
缩放变换
- 错切变换
错切变换
像素块分析
Draw the bitmap through the mesh, where mesh vertices are evenly distributed across the bitmap. There are meshWidth+1 vertices across, and meshHeight+1 vertices down. The verts array is accessed in row-major order, so that the first meshWidth+1 vertices are distributed across the top of the bitmap from left to right.
drawBitmapMesh()将图像分成了一个个的小块，然后通过改变每一个图像小块来修改整个图像。
实例：旗帜飘动的效果
public class FlagBitmapMeshView extends View {
private final int WIDTH = 200;
private final int HEIGHT = 200;
private int COUNT = (WIDTH + 1) * (HEIGHT + 1);
private float[] verts = new float[COUNT * 2];
private float[] orig = new float[COUNT * 2];
private Bitmap bitmap;
private float A;
private float k = 1;
public FlagBitmapMeshView(Context context) {
super(context);
initView(context);
}
public FlagBitmapMeshView(Context context, AttributeSet attrs) {
super(context, attrs);
initView(context);
}
public FlagBitmapMeshView(Context context, AttributeSet attrs,
int defStyleAttr) {
super(context, attrs, defStyleAttr);
initView(context);
}
private void initView(Context context) {
setFocusable(true);
bitmap = BitmapFactory.decodeResource(context.getResources(),
R.drawable.test);
float bitmapWidth = bitmap.getWidth();
float bitmapHeight = bitmap.getHeight();
int index = 0;
for (int y = 0; y <= HEIGHT; y++) {
float fy = bitmapHeight * y / HEIGHT;
for (int x = 0; x <= WIDTH; x++) {
float fx = bitmapWidth * x / WIDTH;
orig[index * 2 + 0] = verts[index * 2 + 0] = fx;
orig[index * 2 + 1] = verts[index * 2 + 1] = fy + 100;
index += 1;
}
}
A = 50;
}
@Override
protected void onDraw(Canvas canvas) {
flagWave();
k += 0.1F;
canvas.drawBitmapMesh(bitmap, WIDTH, HEIGHT,
verts, 0, null, 0, null);
invalidate();
}
private void flagWave() {
for (int j = 0; j <= HEIGHT; j++) {
for (int i = 0; i <= WIDTH; i++) {
verts[(j * (WIDTH + 1) + i) * 2 + 0] += 0;
float offsetY =
(float) Math.sin((float) i / WIDTH * 2 * Math.PI +
Math.PI * k);
verts[(j * (WIDTH + 1) + i) * 2 + 1] =
orig[(j * WIDTH + i) * 2 + 1] + offsetY * A;
}
}
}
}
