[cogl-clip-stack] Support pushing rectangles onto the stack using window coords

Previously clipping could only be specified in object coordinates, now
rectangles can also be pushed in window coordinates.

Internally rectangles pushed this way are intersected and then clipped using
scissoring.  We also transparently try to convert rectangles pushed in
object coordinates into window coordinates as we anticipate the scissoring
path will be faster then the clip planes and undoubtably it will be faster
than using the stencil buffer.

clutter/cogl/cogl.h.in

@@ -490,6 +490,27 @@ void            cogl_set_source_texture       (CoglHandle texture_handle);
  * intersected with the previous region.
  */
 
+/**
+ * cogl_clip_push_window_rect:
+ * @x_offset: left edge of the clip rectangle in window coordinates
+ * @y_offset: top edge of the clip rectangle in window coordinates
+ * @width: width of the clip rectangle
+ * @height: height of the clip rectangle
+ *
+ * Specifies a rectangular clipping area for all subsequent drawing
+ * operations. Any drawing commands that extend outside the rectangle
+ * will be clipped so that only the portion inside the rectangle will
+ * be displayed. The rectangle dimensions are not transformed by the
+ * current model-view matrix.
+ *
+ * The rectangle is intersected with the current clip region. To undo
+ * the effect of this function, call cogl_clip_pop().
+ */
+void            cogl_clip_push_window_rect    (float x_offset,
+                                               float y_offset,
+                                               float width,
+                                               float height);
+
 /**
  * cogl_clip_push:
  * @x_offset: left edge of the clip rectangle

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

@@ -26,10 +26,14 @@
 #endif
 
 #include <string.h>
+
+#include <glib.h>
+
 #include "cogl.h"
 #include "cogl-clip-stack.h"
 #include "cogl-primitives.h"
 #include "cogl-context.h"
+#include "cogl-internal.h"
 
 /* These are defined in the particular backend (float in GL vs fixed
    in GL ES) */
@@ -55,11 +59,13 @@ void _cogl_set_matrix (const CoglMatrix *matrix);
 typedef struct _CoglClipStack CoglClipStack;
 
 typedef struct _CoglClipStackEntryRect CoglClipStackEntryRect;
+typedef struct _CoglClipStackEntryWindowRect CoglClipStackEntryWindowRect;
 typedef struct _CoglClipStackEntryPath CoglClipStackEntryPath;
 
 typedef enum
   {
     COGL_CLIP_STACK_RECT,
+    COGL_CLIP_STACK_WINDOW_RECT,
     COGL_CLIP_STACK_PATH
   } CoglClipStackEntryType;
 
@@ -70,7 +76,7 @@ struct _CoglClipStack
 
 struct _CoglClipStackEntryRect
 {
-  CoglClipStackEntryType     type;
+  CoglClipStackEntryType type;
 
   /* The rectangle for this clip */
   float                  x_offset;
@@ -82,20 +88,126 @@ struct _CoglClipStackEntryRect
   CoglMatrix             matrix;
 };
 
+struct _CoglClipStackEntryWindowRect
+{
+  CoglClipStackEntryType type;
+
+  /* The window space rectangle for this clip */
+  float                  x0;
+  float                  y0;
+  float                  x1;
+  float                  y1;
+};
+
 struct _CoglClipStackEntryPath
 {
-  CoglClipStackEntryType     type;
+  CoglClipStackEntryType type;
 
   /* The matrix that was current when the clip was set */
-  CoglMatrix                 matrix;
+  CoglMatrix             matrix;
 
   floatVec2              path_nodes_min;
   floatVec2              path_nodes_max;
 
-  guint                      path_size;
-  CoglPathNode               path[1];
+  guint                  path_size;
+  CoglPathNode           path[1];
 };
 
+void
+cogl_clip_push_window_rect (float x_offset,
+	                    float y_offset,
+	                    float width,
+	                    float height)
+{
+  CoglClipStackEntryWindowRect *entry;
+  CoglClipStack *stack;
+  float v[4];
+
+  _COGL_GET_CONTEXT (ctx, NO_RETVAL);
+
+  stack = (CoglClipStack *) ctx->clip.stacks->data;
+
+  cogl_get_viewport (v);
+
+  entry = g_slice_new (CoglClipStackEntryWindowRect);
+
+  /* We convert from coords with (0,0) at top left to coords
+   * with (0,0) at bottom left. */
+  entry->type = COGL_CLIP_STACK_WINDOW_RECT;
+  entry->x0 = x_offset;
+  entry->y0 = v[3] - y_offset - height;
+  entry->x1 = x_offset + width;
+  entry->y1 = v[3] - y_offset;
+
+  /* Store it in the stack */
+  stack->stack_top = g_list_prepend (stack->stack_top, entry);
+
+  ctx->clip.stack_dirty = TRUE;
+}
+
+/* Scale from OpenGL <-1,1> coordinates system to window coordinates
+ * <0,window-size> with (0,0) being top left. */
+#define VIEWPORT_SCALE_X(x, w, width, origin) \
+    ((((((x) / (w)) + 1.0) / 2) * (width)) + (origin))
+#define VIEWPORT_SCALE_Y(y, w, height, origin) \
+    ((height) - (((((y) / (w)) + 1.0) / 2) * (height)) + (origin))
+
+static void
+transform_point (CoglMatrix *matrix_mv,
+                 CoglMatrix *matrix_p,
+                 float *viewport,
+                 float *x,
+                 float *y)
+{
+  float z = 0;
+  float w = 1;
+
+  /* Apply the model view matrix */
+  cogl_matrix_transform_point (matrix_mv, x, y, &z, &w);
+
+  /* Apply the projection matrix */
+  cogl_matrix_transform_point (matrix_p, x, y, &z, &w);
+  /* Apply viewport transform */
+  *x = VIEWPORT_SCALE_X (*x, w, viewport[2], viewport[0]);
+  *y = VIEWPORT_SCALE_Y (*y, w, viewport[3], viewport[1]);
+}
+
+#undef VIEWPORT_SCALE_X
+#undef VIEWPORT_SCALE_Y
+
+/* Try to push a rectangle given in object coordinates as a rectangle in window
+ * coordinates instead of object coordinates */
+gboolean
+try_pushing_rect_as_window_rect (float x_offset,
+	                         float y_offset,
+                                 float width,
+                                 float height)
+{
+  CoglMatrix matrix;
+  CoglMatrix matrix_p;
+  float v[4];
+  float _x0 = x_offset;
+  float _y0 = y_offset;
+  float _x1 = x_offset + width;
+  float _y1 = y_offset + height;
+
+  cogl_get_modelview_matrix (&matrix);
+
+  if (matrix.xy != 0 || matrix.xz != 0 ||
+      matrix.yx != 0 || matrix.yz != 0 ||
+      matrix.zx != 0 || matrix.zy != 0)
+    return FALSE;
+
+  cogl_get_projection_matrix (&matrix_p);
+  cogl_get_viewport (v);
+
+  transform_point (&matrix, &matrix_p, v, &_x0, &_y0);
+  transform_point (&matrix, &matrix_p, v, &_x1, &_y1);
+
+  cogl_clip_push_window_rect (_x0, _y0, _x1 - _x0, _y1 - _y0);
+  return TRUE;
+}
+
 void
 cogl_clip_push (float x_offset,
 	        float y_offset,
@@ -107,6 +219,11 @@ cogl_clip_push (float x_offset,
 
   _COGL_GET_CONTEXT (ctx, NO_RETVAL);
 
+  /* Try and catch window space rectangles so we can redirect to
+   * cogl_clip_push_window_rect which will use scissoring. */
+  if (try_pushing_rect_as_window_rect (x_offset, y_offset, width, height))
+    return;
+
   stack = (CoglClipStack *) ctx->clip.stacks->data;
 
   entry = g_slice_new (CoglClipStackEntryRect);
@@ -167,6 +284,7 @@ cogl_clip_pop (void)
 {
   gpointer entry;
   CoglClipStack *stack;
+  CoglClipStackEntryType type;
 
   _COGL_GET_CONTEXT (ctx, NO_RETVAL);
 
@@ -175,10 +293,13 @@ cogl_clip_pop (void)
   g_return_if_fail (stack->stack_top != NULL);
 
   entry = stack->stack_top->data;
+  type = *(CoglClipStackEntryType *) entry;
 
   /* Remove the top entry from the stack */
-  if (*(CoglClipStackEntryType *) entry == COGL_CLIP_STACK_RECT)
+  if (type == COGL_CLIP_STACK_RECT)
     g_slice_free (CoglClipStackEntryRect, entry);
+  else if (type == COGL_CLIP_STACK_WINDOW_RECT)
+    g_slice_free (CoglClipStackEntryWindowRect, entry);
   else
     g_free (entry);
 
@@ -196,6 +317,10 @@ _cogl_clip_stack_rebuild (void)
   gboolean using_stencil_buffer = FALSE;
   GList *node;
   CoglClipStack *stack;
+  guint scissor_x0 = 0;
+  guint scissor_y0 = 0;
+  guint scissor_x1 = G_MAXUINT;
+  guint scissor_y1 = G_MAXUINT;
 
   _COGL_GET_CONTEXT (ctx, NO_RETVAL);
 
@@ -206,6 +331,7 @@ _cogl_clip_stack_rebuild (void)
 
   _cogl_disable_clip_planes ();
   _cogl_disable_stencil_buffer ();
+  GE (glDisable (GL_SCISSOR_TEST));
 
   /* If the stack is empty then there's nothing else to do */
   if (stack->stack_top == NULL)
@@ -218,8 +344,9 @@ _cogl_clip_stack_rebuild (void)
   for (; node; node = node->prev)
     {
       gpointer entry = node->data;
+      CoglClipStackEntryType type = *(CoglClipStackEntryType *) entry;
 
-      if (*(CoglClipStackEntryType *) entry == COGL_CLIP_STACK_PATH)
+      if (type == COGL_CLIP_STACK_PATH)
         {
           CoglClipStackEntryPath *path = (CoglClipStackEntryPath *) entry;
 
@@ -239,7 +366,7 @@ _cogl_clip_stack_rebuild (void)
           /* We can't use clip planes any more */
           has_clip_planes = FALSE;
         }
-      else
+      else if (type == COGL_CLIP_STACK_RECT)
         {
           CoglClipStackEntryRect *rect = (CoglClipStackEntryRect *) entry;
 
@@ -270,6 +397,16 @@ _cogl_clip_stack_rebuild (void)
 
           cogl_pop_matrix ();
         }
+      else
+        {
+          /* Get the intersection of all window space rectangles in the clip
+           * stack */
+          CoglClipStackEntryWindowRect *window_rect = entry;
+          scissor_x0 = MAX (scissor_x0, window_rect->x0);
+          scissor_y0 = MAX (scissor_y0, window_rect->y0);
+          scissor_x1 = MIN (scissor_x1, window_rect->x1);
+          scissor_y1 = MIN (scissor_y1, window_rect->y1);
+        }
     }
 
   /* Enabling clip planes is delayed to now so that they won't affect
@@ -277,6 +414,18 @@ _cogl_clip_stack_rebuild (void)
   if (using_clip_planes)
     _cogl_enable_clip_planes ();
 
+  if (scissor_x0 >= scissor_x1 || scissor_y0 >= scissor_y1)
+    scissor_x0 = scissor_y0 = scissor_x1 = scissor_y1 = 0;
+
+  if (!(scissor_x0 == 0 && scissor_y0 == 0 &&
+        scissor_x1 == G_MAXUINT && scissor_y1 == G_MAXUINT))
+    {
+      GE (glEnable (GL_SCISSOR_TEST));
+      GE (glScissor (scissor_x0, scissor_y0,
+                     scissor_x1 - scissor_x0,
+                     scissor_y1 - scissor_y0));
+    }
+
   ctx->clip.stencil_used = using_stencil_buffer;
 }
 

clutter/cogl/common/cogl.c

@@ -89,6 +89,8 @@ cogl_clear (const CoglColor *color, gulong buffers)
   fprintf(stderr, "\n ============== Paint Start ================ \n");
 #endif
 
+  cogl_clip_ensure ();
+
   if (buffers & COGL_BUFFER_BIT_COLOR)
     {
       GE( glClearColor (cogl_color_get_red_float (color),