[Mesa-dev] [PATCH 3/3] glsl: simplify ES Vertex/Fragment shader requirements

[Timothy Arceri]

We really just needed to skip the existing ES < 3.1 check if we have
a compute shader, all other scenarios are already covered.

* No shaders is a link error.
* Geom or Tess without Vertex is a link error which means we always
  require a Vertex shader and hence a Fragment shader.
* Finally a Compute shader linked with any other stage is a link error.
---

 This also requires:

 http://patchwork.freedesktop.org/patch/71619/

 src/compiler/glsl/linker.cpp | 56 ++++++++++++++++++++++----------------------
 1 file changed, 28 insertions(+), 28 deletions(-)

diff --git a/src/compiler/glsl/linker.cpp b/src/compiler/glsl/linker.cpp
index 5cd613d..fdfdcaa 100644
--- a/src/compiler/glsl/linker.cpp
+++ b/src/compiler/glsl/linker.cpp
@@ -4565,38 +4565,38 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
    if (!prog->LinkStatus)
       goto done;
 
-   /* OpenGL ES requires that a vertex shader and a fragment shader both be
-    * present in a linked program. GL_ARB_ES2_compatibility doesn't say
+   /* OpenGL ES < 3.1 requires that a vertex shader and a fragment shader both
+    * be present in a linked program. GL_ARB_ES2_compatibility doesn't say
     * anything about shader linking when one of the shaders (vertex or
     * fragment shader) is absent. So, the extension shouldn't change the
     * behavior specified in GLSL specification.
+    *
+    * From OpenGL ES 3.1 specification (7.3 Program Objects):
+    *     "Linking can fail for a variety of reasons as specified in the
+    *     OpenGL ES Shading Language Specification, as well as any of the
+    *     following reasons:
+    *
+    *     ...
+    *
+    *     * program contains objects to form either a vertex shader or
+    *       fragment shader, and program is not separable, and does not
+    *       contain objects to form both a vertex shader and fragment
+    *       shader."
+    *
+    * However, the only scenario in 3.1+ where we don't require them both is
+    * when we have a compute shader. For example:
+    *
+    * - No shaders is a link error.
+    * - Geom or Tess without a Vertex shader is a link error which means we
+    *   always require a Vertex shader and hence a Fragment shader.
+    * - Finally a Compute shader linked with any other stage is a link error.
     */
-   if (!prog->SeparateShader && ctx->API == API_OPENGLES2) {
-      /* With ES < 3.1 one needs to have always vertex + fragment shader. */
-      if (ctx->Version < 31) {
-         if (prog->_LinkedShaders[MESA_SHADER_VERTEX] == NULL) {
-	    linker_error(prog, "program lacks a vertex shader\n");
-         } else if (prog->_LinkedShaders[MESA_SHADER_FRAGMENT] == NULL) {
-	    linker_error(prog, "program lacks a fragment shader\n");
-         }
-      } else {
-         /* From OpenGL ES 3.1 specification (7.3 Program Objects):
-          *     "Linking can fail for a variety of reasons as specified in the
-          *     OpenGL ES Shading Language Specification, as well as any of the
-          *     following reasons:
-          *
-          *     ...
-          *
-          *     * program contains objects to form either a vertex shader or
-          *       fragment shader, and program is not separable, and does not
-          *       contain objects to form both a vertex shader and fragment
-          *       shader."
-          */
-         if (!!prog->_LinkedShaders[MESA_SHADER_VERTEX] ^
-             !!prog->_LinkedShaders[MESA_SHADER_FRAGMENT]) {
-            linker_error(prog, "Program needs to contain both vertex and "
-                         "fragment shaders.\n");
-         }
+   if (!prog->SeparateShader && ctx->API == API_OPENGLES2 &&
+       num_shaders[MESA_SHADER_COMPUTE] == 0) {
+      if (prog->_LinkedShaders[MESA_SHADER_VERTEX] == NULL) {
+	 linker_error(prog, "program lacks a vertex shader\n");
+      } else if (prog->_LinkedShaders[MESA_SHADER_FRAGMENT] == NULL) {
+	 linker_error(prog, "program lacks a fragment shader\n");
       }
    }
 
-- 
2.5.0