main: Refactor _mesa_ReadBuffer.

This could have added a new DD table entry for ReadBuffer that takes an
arbitrary read buffer, but, after looking at the existing DD functions,
Kenneth Graunke recommended that we just skip calling the DD functions in the
case of ARB_direct_state_access.  The DD implementations for ReadBuffer
have limited functionality, especially with respect to
ARB_direct_state_access.

[Fredrik: Call the driver function when fb is the bound read buffer]

Reviewed-by: Fredrik Höglund <fredrik@kde.org>
Signed-off-by: Fredrik Höglund <fredrik@kde.org>

src/mesa/main/buffers.c

@@ -623,11 +623,10 @@ _mesa_update_draw_buffers(struct gl_context *ctx)
  * \param bufferIndex  the numerical index corresponding to 'buffer'
  */
 void
-_mesa_readbuffer(struct gl_context *ctx, GLenum buffer, GLint bufferIndex)
+_mesa_readbuffer(struct gl_context *ctx, struct gl_framebuffer *fb,
+                 GLenum buffer, GLint bufferIndex)
 {
-   struct gl_framebuffer *fb = ctx->ReadBuffer;
-
-   if (_mesa_is_winsys_fbo(fb)) {
+   if ((fb == ctx->ReadBuffer) && _mesa_is_winsys_fbo(fb)) {
       /* Only update the per-context READ_BUFFER state if we're bound to
        * a window-system framebuffer.
        */
@@ -646,23 +645,17 @@ _mesa_readbuffer(struct gl_context *ctx, GLenum buffer, GLint bufferIndex)
  * Called by glReadBuffer to set the source renderbuffer for reading pixels.
  * \param mode color buffer such as GL_FRONT, GL_BACK, etc.
  */
-void GLAPIENTRY
-_mesa_ReadBuffer(GLenum buffer)
+void
+_mesa_read_buffer(struct gl_context *ctx, struct gl_framebuffer *fb,
+                  GLenum buffer, const char *caller)
 {
-   struct gl_framebuffer *fb;
    GLbitfield supportedMask;
    GLint srcBuffer;
-   GET_CURRENT_CONTEXT(ctx);
 
    FLUSH_VERTICES(ctx, 0);
 
    if (MESA_VERBOSE & VERBOSE_API)
-      _mesa_debug(ctx, "glReadBuffer %s\n", _mesa_lookup_enum_by_nr(buffer));
-
-   fb = ctx->ReadBuffer;
-
-   if (MESA_VERBOSE & VERBOSE_API)
-      _mesa_debug(ctx, "glReadBuffer %s\n", _mesa_lookup_enum_by_nr(buffer));
+      _mesa_debug(ctx, "%s %s\n", caller, _mesa_lookup_enum_by_nr(buffer));
 
    if (buffer == GL_NONE) {
       /* This is legal--it means that no buffer should be bound for reading. */
@@ -673,24 +666,34 @@ _mesa_ReadBuffer(GLenum buffer)
       srcBuffer = read_buffer_enum_to_index(buffer);
       if (srcBuffer == -1) {
          _mesa_error(ctx, GL_INVALID_ENUM,
-                     "glReadBuffer(buffer=0x%x)", buffer);
+                     "%s(invalid buffer %s)", caller,
+                     _mesa_lookup_enum_by_nr(buffer));
          return;
       }
       supportedMask = supported_buffer_bitmask(ctx, fb);
       if (((1 << srcBuffer) & supportedMask) == 0) {
          _mesa_error(ctx, GL_INVALID_OPERATION,
-                     "glReadBuffer(buffer=0x%x)", buffer);
+                     "%s(invalid buffer %s)", caller,
+                     _mesa_lookup_enum_by_nr(buffer));
          return;
       }
    }
 
    /* OK, all error checking has been completed now */
 
-   _mesa_readbuffer(ctx, buffer, srcBuffer);
+   _mesa_readbuffer(ctx, fb, buffer, srcBuffer);
 
-   /*
-    * Call device driver function.
-    */
-   if (ctx->Driver.ReadBuffer)
-      (*ctx->Driver.ReadBuffer)(ctx, buffer);
+   /* Call the device driver function only if fb is the bound read buffer */
+   if (fb == ctx->ReadBuffer) {
+      if (ctx->Driver.ReadBuffer)
+         (*ctx->Driver.ReadBuffer)(ctx, buffer);
+   }
+}
+
+
+void GLAPIENTRY
+_mesa_ReadBuffer(GLenum buffer)
+{
+   GET_CURRENT_CONTEXT(ctx);
+   _mesa_read_buffer(ctx, ctx->ReadBuffer, buffer, "glReadBuffer");
 }

src/mesa/main/buffers.h

@@ -57,12 +57,17 @@ _mesa_drawbuffers(struct gl_context *ctx, struct gl_framebuffer *fb,
                   const GLbitfield *destMask);
 
 extern void
-_mesa_readbuffer(struct gl_context *ctx, GLenum buffer, GLint bufferIndex);
+_mesa_readbuffer(struct gl_context *ctx, struct gl_framebuffer *fb,
+                 GLenum buffer, GLint bufferIndex);
 
 extern void
 _mesa_update_draw_buffers(struct gl_context *ctx);
 
 
+extern void
+_mesa_read_buffer(struct gl_context *ctx, struct gl_framebuffer *fb,
+                  GLenum buffer, const char *caller);
+
 extern void GLAPIENTRY
 _mesa_ReadBuffer( GLenum mode );
 

src/mesa/main/context.c

@@ -1579,7 +1579,7 @@ handle_first_current(struct gl_context *ctx)
             bufferIndex = BUFFER_FRONT_LEFT;
          }
 
-         _mesa_readbuffer(ctx, buffer, bufferIndex);
+         _mesa_readbuffer(ctx, ctx->ReadBuffer, buffer, bufferIndex);
       }
    }