[Mesa-dev] [PATCH 1/2] mesa: Ensure that transform feedback refers to the correct program.

[Paul Berry]

Previous to this patch, the _mesa_{Begin,Resume}TransformFeedback
functions were using ctx->Shader.CurrentProgram[MESA_SHADER_VERTEX] to
find the program that would be the source of transform feedback data.
This isn't correct--if there's a geometry shader present it should be
ctx->Shader.CurrentProgram[MESA_SHADER_GEOMETRY].  (These might be
different if separate shader objects are in use).

This patch creates a function get_xfb_source(), which figures out the
correct program to use based on GL state, and updates
_mesa_{Begin,Resume}TransformFeedback to call it.  get_xfb_source() is
written in terms of the gl_shader_stage enum, so it should not need
modification when we add tessellation shaders in the future.  It also
creates a new driver flag, NewTransformFeedbackProg, which is flagged
whenever this program changes.

To reduce future confusion, this patch also rewords some comments and
error message text to avoid referring to vertex shaders.
---
 src/mesa/main/mtypes.h            |  8 ++++--
 src/mesa/main/transformfeedback.c | 52 +++++++++++++++++++++++++++++----------
 2 files changed, 45 insertions(+), 15 deletions(-)

diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
index 3dd9678..7fd3298 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -1815,8 +1815,9 @@ struct gl_transform_feedback_object
 
    /**
     * The shader program active when BeginTransformFeedback() was called.
-    * When active and unpaused, this equals
-    * ctx->Shader.CurrentProgram[MESA_SHADER_VERTEX].
+    * When active and unpaused, this equals ctx->Shader.CurrentProgram[stage],
+    * where stage is the pipeline stage that is the source of data for
+    * transform feedback.
     */
    struct gl_shader_program *shader_program;
 
@@ -3779,6 +3780,9 @@ struct gl_driver_flags
    /** gl_context::TransformFeedback::CurrentObject */
    GLbitfield NewTransformFeedback;
 
+   /** gl_context::TransformFeedback::CurrentObject::shader_program */
+   GLbitfield NewTransformFeedbackProg;
+
    /** gl_context::RasterDiscard */
    GLbitfield NewRasterizerDiscard;
 
diff --git a/src/mesa/main/transformfeedback.c b/src/mesa/main/transformfeedback.c
index 74897ba..9376a9e 100644
--- a/src/mesa/main/transformfeedback.c
+++ b/src/mesa/main/transformfeedback.c
@@ -24,7 +24,7 @@
 
 
 /*
- * Vertex transform feedback support.
+ * Transform feedback support.
  *
  * Authors:
  *   Brian Paul
@@ -376,25 +376,48 @@ _mesa_compute_max_transform_feedback_vertices(
  **/
 
 
+/**
+ * Figure out which stage of the pipeline is the source of transform feedback
+ * data given the current context state, and return its gl_shader_program.
+ *
+ * If no active program can generate transform feedback data (i.e. no vertex
+ * shader is active), returns NULL.
+ */
+static struct gl_shader_program *
+get_xfb_source(struct gl_context *ctx)
+{
+   int i;
+   for (i = MESA_SHADER_FRAGMENT - 1; i >= MESA_SHADER_VERTEX; i--) {
+      if (ctx->Shader.CurrentProgram[i] != NULL)
+         return ctx->Shader.CurrentProgram[i];
+   }
+   return NULL;
+}
+
+
 void GLAPIENTRY
 _mesa_BeginTransformFeedback(GLenum mode)
 {
    struct gl_transform_feedback_object *obj;
-   struct gl_transform_feedback_info *info;
+   struct gl_transform_feedback_info *info = NULL;
+   struct gl_shader_program *source;
    GLuint i;
    unsigned vertices_per_prim;
    GET_CURRENT_CONTEXT(ctx);
 
    obj = ctx->TransformFeedback.CurrentObject;
 
-   if (ctx->Shader.CurrentProgram[MESA_SHADER_VERTEX] == NULL) {
+   /* Figure out what pipeline stage is the source of data for transform
+    * feedback.
+    */
+   source = get_xfb_source(ctx);
+   if (source == NULL) {
       _mesa_error(ctx, GL_INVALID_OPERATION,
                   "glBeginTransformFeedback(no program active)");
       return;
    }
 
-   info =
-      &ctx->Shader.CurrentProgram[MESA_SHADER_VERTEX]->LinkedTransformFeedback;
+   info = &source->LinkedTransformFeedback;
 
    if (info->NumOutputs == 0) {
       _mesa_error(ctx, GL_INVALID_OPERATION,
@@ -452,7 +475,10 @@ _mesa_BeginTransformFeedback(GLenum mode)
       obj->GlesRemainingPrims = max_vertices / vertices_per_prim;
    }
 
-   obj->shader_program = ctx->Shader.CurrentProgram[MESA_SHADER_VERTEX];
+   if (obj->shader_program != source) {
+      ctx->NewDriverState |= ctx->DriverFlags.NewTransformFeedbackProg;
+      obj->shader_program = source;
+   }
 
    assert(ctx->Driver.BeginTransformFeedback);
    ctx->Driver.BeginTransformFeedback(ctx, mode, obj);
@@ -519,7 +545,7 @@ bind_buffer_range(struct gl_context *ctx, GLuint index,
 
 
 /**
- * Specify a buffer object to receive vertex shader results.  Plus,
+ * Specify a buffer object to receive transform feedback results.  Plus,
  * specify the starting offset to place the results, and max size.
  * Called from the glBindBufferRange() function.
  */
@@ -563,7 +589,7 @@ _mesa_bind_buffer_range_transform_feedback(struct gl_context *ctx,
 
 
 /**
- * Specify a buffer object to receive vertex shader results.
+ * Specify a buffer object to receive transform feedback results.
  * As above, but start at offset = 0.
  * Called from the glBindBufferBase() function.
  */
@@ -592,7 +618,7 @@ _mesa_bind_buffer_base_transform_feedback(struct gl_context *ctx,
 
 
 /**
- * Specify a buffer object to receive vertex shader results, plus the
+ * Specify a buffer object to receive transform feedback results, plus the
  * offset in the buffer to start placing results.
  * This function is part of GL_EXT_transform_feedback, but not GL3.
  */
@@ -647,7 +673,7 @@ _mesa_BindBufferOffsetEXT(GLenum target, GLuint index, GLuint buffer,
 
 
 /**
- * This function specifies the vertex shader outputs to be written
+ * This function specifies the transform feedback outputs to be written
  * to the feedback buffer(s), and in what order.
  */
 void GLAPIENTRY
@@ -757,7 +783,7 @@ _mesa_TransformFeedbackVaryings(GLuint program, GLsizei count,
 
 
 /**
- * Get info about the vertex shader's outputs which are to be written
+ * Get info about the transform feedback outputs which are to be written
  * to the feedback buffer(s).
  */
 void GLAPIENTRY
@@ -994,9 +1020,9 @@ _mesa_ResumeTransformFeedback(void)
     *  the program object being used by the current transform feedback object
     *  is not active."
     */
-   if (obj->shader_program != ctx->Shader.CurrentProgram[MESA_SHADER_VERTEX]) {
+   if (obj->shader_program != get_xfb_source(ctx)) {
       _mesa_error(ctx, GL_INVALID_OPERATION,
-                  "glResumeTransformFeedback(wrong vertex program bound)");
+                  "glResumeTransformFeedback(wrong program bound)");
       return;
    }
 
-- 
1.8.5.3