- y_align *= 32;
-
- /* From the Ivy Bridge PRM, Vol2 Part1 11.7 "MCS Buffer for Render
- * Target(s)", beneath the "Fast Color Clear" bullet (p327):
- *
- * In order to optimize the performance MCS buffer (when bound to
- * 1X RT) clear similarly to MCS buffer clear for MSRT case,
- * clear rect is required to be scaled by the following factors
- * in the horizontal and vertical directions:
- *
- * The X and Y scale down factors in the table that follows are each
- * equal to half the alignment value computed above.
- */
- x_scaledown = x_align / 2;
- y_scaledown = y_align / 2;
-
- /* From BSpec: 3D-Media-GPGPU Engine > 3D Pipeline > Pixel > Pixel
- * Backend > MCS Buffer for Render Target(s) [DevIVB+] > Table "Color
- * Clear of Non-MultiSampled Render Target Restrictions":
- *
- * Clear rectangle must be aligned to two times the number of
- * pixels in the table shown below due to 16x16 hashing across the
- * slice.
- */
- x_align *= 2;
- y_align *= 2;
- } else {
- /* From the Ivy Bridge PRM, Vol2 Part1 11.7 "MCS Buffer for Render
- * Target(s)", beneath the "MSAA Compression" bullet (p326):
- *
- * Clear pass for this case requires that scaled down primitive
- * is sent down with upper left co-ordinate to coincide with
- * actual rectangle being cleared. For MSAA, clear rectangle’s
- * height and width need to as show in the following table in
- * terms of (width,height) of the RT.
- *
- * MSAA Width of Clear Rect Height of Clear Rect
- * 2X Ceil(1/8*width) Ceil(1/2*height)
- * 4X Ceil(1/8*width) Ceil(1/2*height)
- * 8X Ceil(1/2*width) Ceil(1/2*height)
- * 16X width Ceil(1/2*height)
- *
- * The text "with upper left co-ordinate to coincide with actual
- * rectangle being cleared" is a little confusing--it seems to imply
- * that to clear a rectangle from (x,y) to (x+w,y+h), one needs to
- * feed the pipeline using the rectangle (x,y) to
- * (x+Ceil(w/N),y+Ceil(h/2)), where N is either 2 or 8 depending on
- * the number of samples. Experiments indicate that this is not
- * quite correct; actually, what the hardware appears to do is to
- * align whatever rectangle is sent down the pipeline to the nearest
- * multiple of 2x2 blocks, and then scale it up by a factor of N
- * horizontally and 2 vertically. So the resulting alignment is 4
- * vertically and either 4 or 16 horizontally, and the scaledown
- * factor is 2 vertically and either 2 or 8 horizontally.
- */
- switch (mt->num_samples) {
- case 2:
- case 4:
- x_scaledown = 8;
- break;
- case 8:
- x_scaledown = 2;
- break;
- case 16:
- x_scaledown = 1;
- break;
- default:
- unreachable("Unexpected sample count for fast clear");
- }
- y_scaledown = 2;
- x_align = x_scaledown * 2;
- y_align = y_scaledown * 2;