[Mesa-dev] [PATCH] anv: Port the guardband setting code from i965

[Jason Ekstrand]

---
 src/intel/vulkan/gen8_cmd_buffer.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/src/intel/vulkan/gen8_cmd_buffer.c b/src/intel/vulkan/gen8_cmd_buffer.c
index 3e4aa9b..6b56d06 100644
--- a/src/intel/vulkan/gen8_cmd_buffer.c
+++ b/src/intel/vulkan/gen8_cmd_buffer.c
@@ -44,6 +44,22 @@ gen8_cmd_buffer_emit_viewport(struct anv_cmd_buffer *cmd_buffer)
    for (uint32_t i = 0; i < count; i++) {
       const VkViewport *vp = &viewports[i];
 
+      /* According to the "Vertex X,Y Clamping and Quantization" section of
+       * the Strips and Fans documentation, objects must not have a
+       * screen-space extents of over 8192 pixels, or they may be
+       * mis-rasterized.  The maximum screen space coordinates of a small
+       * object may larger, but we have no way to enforce the object size
+       * other than through clipping.
+       *
+       * If you're surprised that we set clip to -gbx to +gbx and it seems
+       * like we'll end up with 16384 wide, note that for a 8192-wide render
+       * target, we'll end up with a normal (-1, 1) clip volume that just
+       * covers the drawable.
+       */
+      const float maximum_guardband_extent = 8192;
+      const float gbx = maximum_guardband_extent / vp->width;
+      const float gby = maximum_guardband_extent / vp->height;
+
       /* The gen7 state struct has just the matrix and guardband fields, the
        * gen8 struct adds the min/max viewport fields. */
       struct GENX(SF_CLIP_VIEWPORT) sf_clip_viewport = {
@@ -53,10 +69,10 @@ gen8_cmd_buffer_emit_viewport(struct anv_cmd_buffer *cmd_buffer)
          .ViewportMatrixElementm30 = vp->x + vp->width / 2,
          .ViewportMatrixElementm31 = vp->y + vp->height / 2,
          .ViewportMatrixElementm32 = 0.0,
-         .XMinClipGuardband = -1.0f,
-         .XMaxClipGuardband = 1.0f,
-         .YMinClipGuardband = -1.0f,
-         .YMaxClipGuardband = 1.0f,
+         .XMinClipGuardband = -gbx,
+         .XMaxClipGuardband = gbx,
+         .YMinClipGuardband = -gbx,
+         .YMaxClipGuardband = gbx,
          .XMinViewPort = vp->x,
          .XMaxViewPort = vp->x + vp->width - 1,
          .YMinViewPort = vp->y,
-- 
2.5.0.400.gff86faf