......
......
void SurfaceTexture::computeTransformMatrix(float outTransform[16], const sp<GraphicBuffer>& buf,
                                            const Rect& cropRect, uint32_t transform,
                                            bool filtering) {
  ......
    if (!cropRect.isEmpty() && buf.get()) {
        float tx = 0.0f, ty = 0.0f, sx = 1.0f, sy = 1.0f;
        float bufferWidth = buf->getWidth();
        float bufferHeight = buf->getHeight();
        float shrinkAmount = 0.0f;
        if (filtering) {
            // In order to prevent bilinear sampling beyond the edge of the
            // crop rectangle we may need to shrink it by 2 texels in each
            // dimension.  Normally this would just need to take 1/2 a texel
            // off each end, but because the chroma channels of YUV420 images
            // are subsampled we may need to shrink the crop region by a whole
            // texel on each side.
            switch (buf->getPixelFormat()) {
                case PIXEL_FORMAT_RGBA_8888:
                case PIXEL_FORMAT_RGBX_8888:
                case PIXEL_FORMAT_RGBA_FP16:
                case PIXEL_FORMAT_RGBA_1010102:
                case PIXEL_FORMAT_RGB_888:
                case PIXEL_FORMAT_RGB_565:
                case PIXEL_FORMAT_BGRA_8888:
                    // We know there's no subsampling of any channels, so we
                    // only need to shrink by a half a pixel.
                    shrinkAmount = 0.5;
                    break;

                default:
                    // If we don't recognize the format, we must assume the
                    // worst case (that we care about), which is YUV420.
                    shrinkAmount = 1.0;
                    break;
            }
        }

        // Only shrink the dimensions that are not the size of the buffer.
        if (cropRect.width() < bufferWidth) {
            tx = (float(cropRect.left) + shrinkAmount) / bufferWidth;
            sx = (float(cropRect.width()) - (2.0f * shrinkAmount)) / bufferWidth;
        }
        if (cropRect.height() < bufferHeight) {
            ty = (float(bufferHeight - cropRect.bottom) + shrinkAmount) / bufferHeight;
            sy = (float(cropRect.height()) - (2.0f * shrinkAmount)) / bufferHeight;
        }

        mat4 crop(sx, 0, 0, 0, 0, sy, 0, 0, 0, 0, 1, 0, tx, ty, 0, 1);
        xform = crop * xform;
    }
  ......
}
......
......