cogl-debug: Add a debug option for tracing clipping

This adds a COGL_DEBUG=clipping option that reports how the clip is
being flushed. This is needed to determine whether the scissor,
stencil clip planes or software clipping is being used.

clutter/cogl/cogl/cogl-clip-stack.c

@@ -597,6 +597,8 @@ _cogl_clip_stack_flush (CoglClipStack *stack)
   /* If the stack is empty then there's nothing else to do */
   if (stack == NULL)
     {
+      COGL_NOTE (CLIPPING, "Flushed empty clip stack");
+
       ctx->current_clip_stack_uses_stencil = FALSE;
       GE (glDisable (GL_SCISSOR_TEST));
       return;
@@ -636,6 +638,10 @@ _cogl_clip_stack_flush (CoglClipStack *stack)
         }
     }
 
+  COGL_NOTE (CLIPPING, "Flushing scissor to (%i, %i, %i, %i)",
+             scissor_x0, scissor_y0,
+             scissor_x1, scissor_y1);
+
   GE (glEnable (GL_SCISSOR_TEST));
   GE (glScissor (scissor_x0, scissor_y_start,
                  scissor_x1 - scissor_x0,
@@ -651,6 +657,8 @@ _cogl_clip_stack_flush (CoglClipStack *stack)
         {
           CoglClipStackPath *path_entry = (CoglClipStackPath *) entry;
 
+          COGL_NOTE (CLIPPING, "Adding stencil clip for path");
+
           _cogl_matrix_stack_push (modelview_stack);
           _cogl_matrix_stack_set (modelview_stack, &path_entry->matrix);
 
@@ -677,6 +685,8 @@ _cogl_clip_stack_flush (CoglClipStack *stack)
                  them then use that instead */
               if (has_clip_planes)
                 {
+                  COGL_NOTE (CLIPPING, "Adding clip planes clip for rectangle");
+
                   set_clip_planes (rect->x0,
                                    rect->y0,
                                    rect->x1,
@@ -687,6 +697,8 @@ _cogl_clip_stack_flush (CoglClipStack *stack)
                 }
               else
                 {
+                  COGL_NOTE (CLIPPING, "Adding stencil clip for rectangle");
+
                   add_stencil_clip_rectangle (rect->x0,
                                               rect->y0,
                                               rect->x1,

clutter/cogl/cogl/cogl-debug-options.h

@@ -174,3 +174,8 @@ OPT (DISABLE_FAST_READ_PIXEL,
      "Disable read pixel optimization",
      "Disable optimization for reading 1px for simple "
      "scenes of opaque rectangles")
+OPT (CLIPPING,
+     "Cogl Tracing",
+     "clipping",
+     "Trace clipping",
+     "Logs information about how Cogl is implementing clipping")

clutter/cogl/cogl/cogl-debug.c

@@ -54,7 +54,8 @@ static const GDebugKey cogl_log_debug_keys[] = {
   { "show-source", COGL_DEBUG_SHOW_SOURCE},
   { "offscreen", COGL_DEBUG_OFFSCREEN },
   { "texture-pixmap", COGL_DEBUG_TEXTURE_PIXMAP },
-  { "bitmap", COGL_DEBUG_BITMAP }
+  { "bitmap", COGL_DEBUG_BITMAP },
+  { "clipping", COGL_DEBUG_CLIPPING }
 };
 static const int n_cogl_log_debug_keys =
   G_N_ELEMENTS (cogl_log_debug_keys);

clutter/cogl/cogl/cogl-debug.h

@@ -62,6 +62,7 @@ typedef enum {
   COGL_DEBUG_DISABLE_SOFTWARE_CLIP,
   COGL_DEBUG_DISABLE_PROGRAM_CACHES,
   COGL_DEBUG_DISABLE_FAST_READ_PIXEL,
+  COGL_DEBUG_CLIPPING,
 
   COGL_DEBUG_N_FLAGS
 } CoglDebugFlags;

clutter/cogl/cogl/cogl-journal.c

@@ -1046,6 +1046,8 @@ maybe_software_clip_entries (CoglJournalEntry      *batch_start,
 
   /* If we make it here then we know we can software clip the entire batch */
 
+  COGL_NOTE (CLIPPING, "Software clipping a batch of length %i", batch_len);
+
   for (entry_num = 0; entry_num < batch_len; entry_num++)
     {
       CoglJournalEntry *journal_entry = batch_start + entry_num;