mesa, st/mesa: fix gl_FragCoord with FBOs in Gallium

gl_FragCoord.y needs to be flipped upside down if a FBO is bound.

This fixes:
- piglit/fbo-fragcoord
- https://bugs.freedesktop.org/show_bug.cgi?id=29420

Here I add a new program state STATE_FB_WPOS_Y_TRANSFORM, which is set based
on whether a FBO is bound. The state contains a pair of transformations.
It can be either (XY=identity, ZW=transformY) if a FBO is bound,
or (XY=transformY, ZW=identity) otherwise, where identity = (1, 0),
transformY = (-1, height-1).

A classic driver (or st/mesa) may, based on some other state, choose whether
to use XY or ZW, thus negate the conditional "if (is a FBO bound) ...".
The reason for this is that a Gallium driver is allowed to only support WPOS
relative to either the lower left or the upper left corner, so we must flip
the Y axis accordingly again. (the "invert" parameter in emit_wpos_inversion)

NOTE: This is a candidate for the 7.9 branch.

Signed-off-by: Marek Olšák <[email protected]>
Signed-off-by: Brian Paul <[email protected]>

1 files changed, 22 insertions, 0 deletions

diff --git a/src/mesa/program/prog_statevars.c b/src/mesa/program/prog_statevars.c
index baac29ff0dd..83bd3727f33 100644
--- a/src/mesa/program/prog_statevars.c
+++ b/src/mesa/program/prog_statevars.c
@@ -572,6 +572,24 @@ _mesa_fetch_state(struct gl_context *ctx, const gl_state_index state[],
          value[3] = 0.0F;
          return;
 
+      case STATE_FB_WPOS_Y_TRANSFORM:
+         /* A driver may negate this conditional by using ZW swizzle
+          * instead of XY (based on e.g. some other state). */
+         if (ctx->DrawBuffer->Name != 0) {
+            /* Identity (XY) followed by flipping Y upside down (ZW). */
+            value[0] = 1.0F;
+            value[1] = 0.0F;
+            value[2] = -1.0F;
+            value[3] = (GLfloat) (ctx->DrawBuffer->Height - 1);
+         } else {
+            /* Flipping Y upside down (XY) followed by identity (ZW). */
+            value[0] = -1.0F;
+            value[1] = (GLfloat) (ctx->DrawBuffer->Height - 1);
+            value[2] = 1.0F;
+            value[3] = 0.0F;
+         }
+         return;
+
       case STATE_ROT_MATRIX_0:
          {
             const int unit = (int) state[2];
@@ -695,6 +713,7 @@ _mesa_program_state_flags(const gl_state_index state[STATE_LENGTH])
          return _NEW_PIXEL;
 
       case STATE_FB_SIZE:
+      case STATE_FB_WPOS_Y_TRANSFORM:
          return _NEW_BUFFERS;
 
       default:
@@ -900,6 +919,9 @@ append_token(char *dst, gl_state_index k)
    case STATE_FB_SIZE:
       append(dst, "FbSize");
       break;
+   case STATE_FB_WPOS_Y_TRANSFORM:
+      append(dst, "FbWposYTransform");
+      break;
    case STATE_ROT_MATRIX_0:
       append(dst, "rotMatrixRow0");
       break;