@Override
public void onDrawScreen(Canvas canvas, int screen, int offset) {
final DrawFilter filter = canvas.getDrawFilter();
requestQuality(canvas, GridScreenEffector.DRAW_QUALITY_HIGH);
final GridScreenContainer container = mContainer;
final int row = container.getCellRow();
final int col = container.getCellCol();
int index = row * col * screen;
final int end = Math.min(container.getCellCount(), index + row * col);
final int count = end - index;
if (count <= 0) {
return;
}
float t = offset * mRatio;
final float dAngle = -360.f / count;
final double dRad = Math.toRadians(dAngle);
final float sin = (float) Math.sin(dRad);
final float cos = (float) Math.cos(dRad);
float iconDstX = mRadius, iconDstY = 0, iconDstAngle = -90;
if (count == 1) {
iconDstX = 0; // 只有一个的时候把它画在圆心处
iconDstAngle = -360;
}
canvas.translate(mCenterX, mCenterY);
final boolean isScrollAtEnd = mScroller.isScrollAtEnd();
if (isScrollAtEnd) {
t *= 1.5f; // 这样在两端的时候更容易组成圈
}
// 以下注释的代码是对cell做包围盒裁剪的，
// 如果cell的内部结构比较简单，其实优化作用不明显
float sinWheelAngle = 0, cosWheelAngle = 1;
if (t > 1) {
sinWheelAngle = (float) Math.sin((Math.PI * 0.5) * (t - 1));
cosWheelAngle = (float) Math.cos((Math.PI * 0.5) * (t - 1));
canvas.rotate(90 * (t - 1));
t = 1;
} else if (t < -1) {
sinWheelAngle = (float) Math.sin((Math.PI * 0.5) * (t + 1));
cosWheelAngle = (float) Math.cos((Math.PI * 0.5) * (t + 1));
canvas.rotate(90 * (t + 1));
t = 1;
} else if (t < 0) {
t = -t;
}
float t1 = t, t2 = t;
if (isScrollAtEnd) {
// 修改插值方式，使在两端恢复时动作更平滑
t1 = ACC_INTERPOLATOR.getInterpolation(t);
t2 = DEC_INTERPOLATOR.getInterpolation(t);
}
final int cellWidth = container.getCellWidth();
final int cellHeight = container.getCellHeight();
final int paddingLeft = container.getPaddingLeft();
final int paddingTop = container.getPaddingTop();
final int cellCenterX = cellWidth / 2;
final int cellCenterY = cellHeight / 2;
final int cellRadius = (int) (Math.hypot(cellWidth, cellHeight) * 0.5) + 2;
// 计算物理屏幕在当前坐标系的左右边界值
final float screenLeft = -mCenterX - offset;
final float screenRight = mCenterX - offset;
for (int i = 0, cellY = paddingTop + cellCenterY; i < row && index < end; ++i) {
for (int j = 0, cellX = paddingLeft + cellCenterX; j < col && index < end; ++j, ++index) {
final float x = interpolate(cellX - mCenterX, iconDstX, t1);
final float y = interpolate(cellY - mCenterY, iconDstY, t1);
final float x2 = x * cosWheelAngle - y * sinWheelAngle;
if (x2 - cellRadius < screenRight && x2 + cellRadius >= screenLeft) {
final float a = interpolate(0, iconDstAngle, t2);
canvas.save();
canvas.translate(x, y);
canvas.rotate(a);
canvas.translate(-cellCenterX, -cellCenterY);
container.drawGridCell(canvas, index);
canvas.restore();
}
final float xBak = iconDstX;
iconDstX = cos * xBak - sin * iconDstY;
iconDstY = sin * xBak + cos * iconDstY;
iconDstAngle += dAngle;
cellX += cellWidth;
}
cellY += cellHeight;
}
canvas.setDrawFilter(filter); // restore filter
}