[mutter/wip/carlosg/clip-regions: 5/6] cogl: Add support for clipping regions

[Carlos Garnacho <carlosg src gnome org>]

commit 311458f9eeabd306c25738eee16c6b7227c3e03e
Author: Carlos Garnacho <carlosg gnome org>
Date:   Tue Jul 30 23:48:45 2019 +0200

    cogl: Add support for clipping regions
    
    This uses the stencil buffer to poke holes in the shape of the
    given cairo_region_t that we will draw through.

 cogl/cogl/cogl-clip-stack.c              | 33 +++++++++++++++++
 cogl/cogl/cogl-clip-stack.h              | 18 ++++++++-
 cogl/cogl/cogl-framebuffer.c             | 17 +++++++++
 cogl/cogl/cogl-framebuffer.h             |  5 +++
 cogl/cogl/driver/gl/cogl-clip-stack-gl.c | 63 ++++++++++++++++++++++++++++++++
 5 files changed, 135 insertions(+), 1 deletion(-)
---
diff --git a/cogl/cogl/cogl-clip-stack.c b/cogl/cogl/cogl-clip-stack.c
index 0461687e7..b4e1a03fa 100644
--- a/cogl/cogl/cogl-clip-stack.c
+++ b/cogl/cogl/cogl-clip-stack.c
@@ -296,6 +296,32 @@ _cogl_clip_stack_push_primitive (CoglClipStack *stack,
   return (CoglClipStack *) entry;
 }
 
+CoglClipStack *
+_cogl_clip_stack_push_region (CoglClipStack   *stack,
+                              CoglMatrixEntry *modelview_entry,
+                              cairo_region_t  *region)
+{
+  CoglClipStack *entry;
+  CoglClipStackRegion *entry_region;
+  cairo_rectangle_int_t bounds;
+
+  entry_region = _cogl_clip_stack_push_entry (stack,
+                                              sizeof (CoglClipStackRegion),
+                                              COGL_CLIP_STACK_REGION);
+  entry = (CoglClipStack *) entry_region;
+
+  cairo_region_get_extents (region, &bounds);
+  entry->bounds_x0 = bounds.x;
+  entry->bounds_x1 = bounds.x + bounds.width;
+  entry->bounds_y0 = bounds.y;
+  entry->bounds_y1 = bounds.y + bounds.height;
+
+  entry_region->matrix_entry = cogl_matrix_entry_ref (modelview_entry);
+  entry_region->region = cairo_region_reference (region);
+
+  return entry;
+}
+
 CoglClipStack *
 _cogl_clip_stack_ref (CoglClipStack *entry)
 {
@@ -337,6 +363,13 @@ _cogl_clip_stack_unref (CoglClipStack *entry)
             g_slice_free1 (sizeof (CoglClipStackPrimitive), entry);
             break;
           }
+        case COGL_CLIP_STACK_REGION:
+          {
+            CoglClipStackRegion *region = (CoglClipStackRegion *) entry;
+            cairo_region_destroy (region->region);
+            g_slice_free1 (sizeof (CoglClipStackRegion), entry);
+            break;
+          }
         default:
           g_assert_not_reached ();
         }
diff --git a/cogl/cogl/cogl-clip-stack.h b/cogl/cogl/cogl-clip-stack.h
index eb2c43282..fedae3f4f 100644
--- a/cogl/cogl/cogl-clip-stack.h
+++ b/cogl/cogl/cogl-clip-stack.h
@@ -48,12 +48,14 @@ typedef struct _CoglClipStack CoglClipStack;
 typedef struct _CoglClipStackRect CoglClipStackRect;
 typedef struct _CoglClipStackWindowRect CoglClipStackWindowRect;
 typedef struct _CoglClipStackPrimitive CoglClipStackPrimitive;
+typedef struct _CoglClipStackRegion CoglClipStackRegion;
 
 typedef enum
   {
     COGL_CLIP_STACK_RECT,
     COGL_CLIP_STACK_WINDOW_RECT,
-    COGL_CLIP_STACK_PRIMITIVE
+    COGL_CLIP_STACK_PRIMITIVE,
+    COGL_CLIP_STACK_REGION,
   } CoglClipStackType;
 
 /* A clip stack consists a list of entries. Each entry has a reference
@@ -162,6 +164,16 @@ struct _CoglClipStackPrimitive
   float bounds_y2;
 };
 
+struct _CoglClipStackRegion
+{
+  CoglClipStack _parent_data;
+
+  /* The matrix that was current when the clip was set */
+  CoglMatrixEntry *matrix_entry;
+
+  cairo_region_t *region;
+};
+
 CoglClipStack *
 _cogl_clip_stack_push_window_rectangle (CoglClipStack *stack,
                                         int x_offset,
@@ -189,6 +201,10 @@ _cogl_clip_stack_push_primitive (CoglClipStack *stack,
                                  CoglMatrixEntry *modelview_entry,
                                  CoglMatrixEntry *projection_entry,
                                  const float *viewport);
+CoglClipStack *
+_cogl_clip_stack_push_region (CoglClipStack   *stack,
+                              CoglMatrixEntry *modelview_entry,
+                              cairo_region_t  *region);
 
 CoglClipStack *
 _cogl_clip_stack_pop (CoglClipStack *stack);
diff --git a/cogl/cogl/cogl-framebuffer.c b/cogl/cogl/cogl-framebuffer.c
index 527fd81ea..687d54b5a 100644
--- a/cogl/cogl/cogl-framebuffer.c
+++ b/cogl/cogl/cogl-framebuffer.c
@@ -1817,6 +1817,23 @@ cogl_framebuffer_push_primitive_clip (CoglFramebuffer *framebuffer,
       COGL_FRAMEBUFFER_STATE_CLIP;
 }
 
+void
+cogl_framebuffer_push_region_clip (CoglFramebuffer *framebuffer,
+                                   cairo_region_t  *region)
+{
+  CoglMatrixEntry *modelview_entry =
+    _cogl_framebuffer_get_modelview_entry (framebuffer);
+
+  framebuffer->clip_stack =
+    _cogl_clip_stack_push_region (framebuffer->clip_stack,
+                                  modelview_entry,
+                                  region);
+
+  if (framebuffer->context->current_draw_buffer == framebuffer)
+    framebuffer->context->current_draw_buffer_changes |=
+      COGL_FRAMEBUFFER_STATE_CLIP;
+}
+
 void
 cogl_framebuffer_pop_clip (CoglFramebuffer *framebuffer)
 {
diff --git a/cogl/cogl/cogl-framebuffer.h b/cogl/cogl/cogl-framebuffer.h
index 08ed3354b..7cc415ea1 100644
--- a/cogl/cogl/cogl-framebuffer.h
+++ b/cogl/cogl/cogl-framebuffer.h
@@ -56,6 +56,7 @@ typedef struct _CoglFramebuffer CoglFramebuffer;
 #include <cogl/cogl-euler.h>
 #include <cogl/cogl-texture.h>
 #include <glib-object.h>
+#include <cairo.h>
 
 G_BEGIN_DECLS
 
@@ -639,6 +640,10 @@ cogl_framebuffer_push_primitive_clip (CoglFramebuffer *framebuffer,
                                       float bounds_x2,
                                       float bounds_y2);
 
+void
+cogl_framebuffer_push_region_clip (CoglFramebuffer *framebuffer,
+                                   cairo_region_t  *region);
+
 /**
  * cogl_framebuffer_pop_clip:
  * @framebuffer: A #CoglFramebuffer pointer
diff --git a/cogl/cogl/driver/gl/cogl-clip-stack-gl.c b/cogl/cogl/driver/gl/cogl-clip-stack-gl.c
index f8a471828..200de00a9 100644
--- a/cogl/cogl/driver/gl/cogl-clip-stack-gl.c
+++ b/cogl/cogl/driver/gl/cogl-clip-stack-gl.c
@@ -260,6 +260,59 @@ add_stencil_clip_rectangle (CoglFramebuffer *framebuffer,
   GE( ctx, glStencilOp (GL_KEEP, GL_KEEP, GL_KEEP) );
 }
 
+static void
+add_stencil_clip_region (CoglFramebuffer *framebuffer,
+                         CoglMatrixEntry *modelview_entry,
+                         cairo_region_t  *region)
+{
+  CoglMatrixStack *projection_stack =
+    _cogl_framebuffer_get_projection_stack (framebuffer);
+  CoglContext *ctx = cogl_framebuffer_get_context (framebuffer);
+  int num_rectangles = cairo_region_num_rectangles (region);
+  int width, height, i;
+
+  /* NB: This can be called while flushing the journal so we need
+   * to be very conservative with what state we change.
+   */
+  _cogl_context_set_current_projection_entry (ctx, &ctx->identity_entry);
+  _cogl_context_set_current_modelview_entry (ctx, &ctx->identity_entry);
+
+  GE( ctx, glEnable (GL_STENCIL_TEST) );
+
+  /* Initially disallow everything */
+  GE( ctx, glClearStencil (0) );
+  GE( ctx, glClear (GL_STENCIL_BUFFER_BIT) );
+
+  /* Punch out a hole to allow the rectangles */
+  GE( ctx, glStencilFunc (GL_NEVER, 0x1, 0x1) );
+  GE( ctx, glStencilOp (GL_REPLACE, GL_REPLACE, GL_REPLACE) );
+
+  width = cogl_framebuffer_get_width (framebuffer);
+  height = cogl_framebuffer_get_height (framebuffer);
+
+  for (i = 0; i < num_rectangles; i++)
+    {
+      cairo_rectangle_int_t rect;
+      float x1, y1, x2, y2;
+
+      cairo_region_get_rectangle (region, i, &rect);
+
+      /* Transform coordinates to identity */
+      x1 = (rect.x * 2.0 / width) - 1;
+      y1 = 1 - (rect.y * 2.0 / height);
+      x2 = ((rect.x + rect.width) * 2.0 / width) -1;
+      y2 = 1 - ((rect.y + rect.height) * 2.0 / height);
+
+      _cogl_rectangle_immediate (framebuffer,
+                                 ctx->stencil_pipeline,
+                                x1, y1, x2, y2);
+    }
+
+  /* Restore the stencil mode */
+  GE( ctx, glStencilFunc (GL_EQUAL, 0x1, 0x1) );
+  GE( ctx, glStencilOp (GL_KEEP, GL_KEEP, GL_KEEP) );
+}
+
 typedef void (*SilhouettePaintCallback) (CoglFramebuffer *framebuffer,
                                          CoglPipeline *pipeline,
                                          void *user_data);
@@ -572,6 +625,16 @@ _cogl_clip_stack_gl_flush (CoglClipStack *stack,
                 }
               break;
             }
+        case COGL_CLIP_STACK_REGION:
+            {
+              CoglClipStackRegion *region = (CoglClipStackRegion *) entry;
+
+              COGL_NOTE (CLIPPING, "Adding stencil clip for region");
+
+              add_stencil_clip_region (framebuffer, region->matrix_entry, region->region);
+              using_stencil_buffer = TRUE;
+              break;
+            }
         case COGL_CLIP_STACK_WINDOW_RECT:
           break;
           /* We don't need to do anything for window space rectangles because