intel: Also get the DRI2 front buffer when doing front buffer reading.

(cherry picked from commit df70d3049a)

src/mesa/drivers/dri/i965/Makefile

@@ -22,6 +22,7 @@ DRIVER_SOURCES = \
 	intel_pixel_bitmap.c \
 	intel_pixel_copy.c \
 	intel_pixel_draw.c \
+	intel_pixel_read.c \
 	intel_state.c \
 	intel_swapbuffers.c \
 	intel_tex.c \

src/mesa/drivers/dri/intel/intel_buffers.c

@@ -345,6 +345,23 @@ intelDrawBuffer(GLcontext * ctx, GLenum mode)
 static void
 intelReadBuffer(GLcontext * ctx, GLenum mode)
 {
+   if ((ctx->DrawBuffer != NULL) && (ctx->DrawBuffer->Name == 0)) {
+      struct intel_context *const intel = intel_context(ctx);
+      const GLboolean was_front_buffer_reading =
+	intel->is_front_buffer_reading;
+
+      intel->is_front_buffer_reading = (mode == GL_FRONT_LEFT)
+	|| (mode == GL_FRONT);
+
+      /* If we weren't front-buffer reading before but we are now, make sure
+       * that the front-buffer has actually been allocated.
+       */
+      if (!was_front_buffer_reading && intel->is_front_buffer_reading) {
+	 intel_update_renderbuffers(intel->driContext,
+				    intel->driContext->driDrawablePriv);
+      }
+   }
+
    if (ctx->ReadBuffer == ctx->DrawBuffer) {
       /* This will update FBO completeness status.
        * A framebuffer will be incomplete if the GL_READ_BUFFER setting

src/mesa/drivers/dri/intel/intel_context.c

@@ -220,7 +220,9 @@ intel_update_renderbuffers(__DRIcontext *context, __DRIdrawable *drawable)
       struct intel_renderbuffer *stencil_rb;
 
       i = 0;
-      if ((intel->is_front_buffer_rendering || !intel_fb->color_rb[1])
+      if ((intel->is_front_buffer_rendering ||
+	   intel->is_front_buffer_reading ||
+	   !intel_fb->color_rb[1])
 	   && intel_fb->color_rb[0]) {
 	 attachments[i++] = __DRI_BUFFER_FRONT_LEFT;
 	 attachments[i++] = intel_bits_per_pixel(intel_fb->color_rb[0]);

src/mesa/drivers/dri/intel/intel_context.h

@@ -295,6 +295,14 @@ struct intel_context
     * easily.
     */
    GLboolean is_front_buffer_rendering;
+   /**
+    * Track whether front-buffer is the current read target.
+    *
+    * This is closely associated with is_front_buffer_rendering, but may
+    * be set separately.  The DRI2 fake front buffer must be referenced
+    * either way.
+    */
+   GLboolean is_front_buffer_reading;
 
    drm_clip_rect_t fboRect;     /**< cliprect for FBO rendering */