[Mesa-dev] [PATCH] i915: fallback when point sprite is enabled while handling varying inputs

[Yuanhan Liu]

The current code would use tex coord to implement varying inputs. If
point sprite is enabled(always enabled in chrome and firefox), the tex
coord would be replaced with the value (x, y, 0, 1) where x and y vary
from 0 to 1. Thus you will find that the value of the varying inputs
doesn't work anymore.

Why chrome(and firefox) would always enable GL_POINT_SPRITE to enable
webglc, if you would ask, here is the answer I find from the code of
chrome at file gpu/command_buffer/service/gles2_cmd_decoder.cc:

  // OpenGL ES 2.0 implicitly enables the desktop GL capability
  // VERTEX_PROGRAM_POINT_SIZE and doesn't expose this enum. This fact
  // isn't well documented; it was discovered in the Khronos OpenGL ES
  // mailing list archives. It also implicitly enables the desktop GL
  // capability GL_POINT_SPRITE to provide access to the gl_PointCoord
  // variable in fragment shaders.
  if (gfx::GetGLImplementation() != gfx::kGLImplementationEGLGLES2) {
    glEnable(GL_VERTEX_PROGRAM_POINT_SIZE);
    glEnable(GL_POINT_SPRITE);
  }

So, fallback when point sprite is enabled while handling varying inputs
before finding a better way to not use tex coord to implement varying
inputs.

This would _really_ fix the following webglc case on pineview this time:
https://cvs.khronos.org/svn/repos/registry/trunk/public/webgl/conformance-suites/1.0.1/conformance/rendering/point-size.html

NOTE: This is a candidate for stable release branches.

Signed-off-by: Yuanhan Liu <yuanhan.liu at linux.intel.com>
---
 src/mesa/drivers/dri/i915/i915_fragprog.c |   23 ++++++++++++++++++++---
 1 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/src/mesa/drivers/dri/i915/i915_fragprog.c b/src/mesa/drivers/dri/i915/i915_fragprog.c
index 5b7e93e..c2390fe 100644
--- a/src/mesa/drivers/dri/i915/i915_fragprog.c
+++ b/src/mesa/drivers/dri/i915/i915_fragprog.c
@@ -132,9 +132,26 @@ src_vector(struct i915_fragment_program *p,
       case FRAG_ATTRIB_VAR0 + 5:
       case FRAG_ATTRIB_VAR0 + 6:
       case FRAG_ATTRIB_VAR0 + 7:
-         src = i915_emit_decl(p, REG_TYPE_T,
-                              T_TEX0 + (source->Index - FRAG_ATTRIB_VAR0),
-                              D0_CHANNEL_ALL);
+         /*
+          * The current code would use tex coord to implement varying inputs.
+          * If point sprite is enabled(always enabled in chrome and firefox),
+          * the tex coord would be replaced with the value (x, y, 0, 1) where
+          * x and y vary from 0 to 1. Thus you will find that the value of the
+          * varying inputs doesn't work anymore.
+          *
+          * So, fallback when point sprite is enabled.
+          *
+          * FIXME: a better way to not use tex coord to add the support of
+          *        varying inputs?
+          */
+         if (p->ctx->Point.PointSprite) {
+             i915_program_error(p, "Point Sprite is enabled while using "
+                                   "tex coord to implement varying inputs");
+         } else {
+             src = i915_emit_decl(p, REG_TYPE_T,
+                                  T_TEX0 + (source->Index - FRAG_ATTRIB_VAR0),
+                                  D0_CHANNEL_ALL);
+         }
          break;
 
       default:
-- 
1.7.7