glamor: Don't write back read only pixmap to fbo.

For those pixmap which has valid fbo and opened as GLAMOR_ACCESS_RO
mode, we don't need to upload the texture back when calling the
glamor_finish_access(). This will get about 10% performance gain.

glamor/glamor_core.c

@@ -332,6 +332,7 @@ glamor_prepare_access(DrawablePtr drawable, glamor_access_t access)
 	return FALSE;
     }
 
+    pixmap_priv->access_mode = access;
     glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, pixmap_priv->fb);
     glPixelStorei(GL_PACK_ALIGNMENT, 1);
     glPixelStorei(GL_PACK_ROW_LENGTH, row_length);
@@ -468,6 +469,9 @@ glamor_finish_access(DrawablePtr drawable)
     if (pixmap->devPrivate.ptr == NULL)
 	return;
 
+    if (pixmap_priv->access_mode == GLAMOR_ACCESS_RO)
+      goto read_only;
+
     stride = pixmap->devKind;
     row_length = (stride * 8) / pixmap->drawable.bitsPerPixel;
     switch (drawable->depth) {
@@ -526,6 +530,7 @@ glamor_finish_access(DrawablePtr drawable)
     glDisableClientState(GL_TEXTURE_COORD_ARRAY);
     glDeleteTextures(1, &tex);
 
+read_only:
     if (GLEW_MESA_pack_invert || glamor_priv->yInverted) {
       glBindBufferARB (GL_PIXEL_PACK_BUFFER_EXT, pixmap_priv->pbo);
       glUnmapBufferARB (GL_PIXEL_PACK_BUFFER_EXT);

glamor/glamor_priv.h

@@ -193,6 +193,7 @@ typedef struct glamor_pixmap_private {
     GLuint fb;
     GLuint pbo;
     enum   glamor_pixmap_type type;
+    glamor_access_t access_mode;
 } glamor_pixmap_private;
 
 extern DevPrivateKey glamor_screen_private_key;