mutter/cogl/cogl-clip-stack.h

/*
 * Cogl
 *
 * An object oriented GL/GLES Abstraction/Utility Layer
 *
 * Copyright (C) 2007,2008,2009,2010 Intel Corporation.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library. If not, see <http://www.gnu.org/licenses/>.
 *
 *
 */

#ifndef __COGL_CLIP_STACK_H
#define __COGL_CLIP_STACK_H

#include "cogl2-path.h"
#include "cogl-matrix.h"

/* The clip stack works like a GSList where only a pointer to the top
   of the stack is stored. The empty clip stack is represented simply
   by the NULL pointer. When an entry is added to or removed from the
   stack the new top of the stack is returned. When an entry is pushed
   a new clip stack entry is created which effectively takes ownership
   of the reference on the old entry. Therefore unrefing the top entry
   effectively loses ownership of all entries in the stack */

typedef struct _CoglClipStack CoglClipStack;
typedef struct _CoglClipStackRect CoglClipStackRect;
typedef struct _CoglClipStackWindowRect CoglClipStackWindowRect;
typedef struct _CoglClipStackPath CoglClipStackPath;

typedef enum
  {
    COGL_CLIP_STACK_RECT,
    COGL_CLIP_STACK_WINDOW_RECT,
    COGL_CLIP_STACK_PATH
  } CoglClipStackType;

/* A clip stack consists a list of entries. Each entry has a reference
 * count and a link to its parent node. The child takes a reference on
 * the parent and the CoglClipStack holds a reference to the top of
 * the stack. There are no links back from the parent to the
 * children. This allows stacks that have common ancestry to share the
 * entries.
 *
 * For example, the following sequence of operations would generate
 * the tree below:
 *
 * CoglClipStack *stack_a = NULL;
 * stack_a = _cogl_clip_stack_push_rectangle (stack_a, ...);
 * stack_a = _cogl_clip_stack_push_rectangle (stack_a, ...);
 * stack_a = _cogl_clip_stack_push_from_path (stack_a, ...);
 * CoglClipStack *stack_b = NULL;
 * stack_b = cogl_clip_stack_push_window_rectangle (stack_b, ...);
 *
 *  stack_a
 *         \ holds a ref to
 *          +-----------+
 *          | path node |
 *          |ref count 1|
 *          +-----------+
 *                       \
 *                        +-----------+  +-----------+
 *       both tops hold   | rect node |  | rect node |
 *       a ref to the     |ref count 2|--|ref count 1|
 *       same rect node   +-----------+  +-----------+
 *                       /
 *          +-----------+
 *          | win. rect |
 *          |ref count 1|
 *          +-----------+
 *         / holds a ref to
 *  stack_b
 *
 */

struct _CoglClipStack
{
  CoglClipStackType  type;

  /* This will be null if there is no parent. If it is not null then
     this node must be holding a reference to the parent */
  CoglClipStack     *parent;

  /* All clip entries have a window-space bounding box which we can
     use to calculate a scissor. The scissor limits the clip so that
     we don't need to do a full stencil clear if the stencil buffer is
     needed. This is stored in Cogl's coordinate space (ie, 0,0 is the
     top left) */
  int                     bounds_x0;
  int                     bounds_y0;
  int                     bounds_x1;
  int                     bounds_y1;

  unsigned int            ref_count;
};

struct _CoglClipStackRect
{
  CoglClipStack     _parent_data;

  /* The rectangle for this clip */
  float                  x0;
  float                  y0;
  float                  x1;
  float                  y1;

  /* If this is true then the clip for this rectangle is entirely
     described by the scissor bounds. This implies that the rectangle
     is screen aligned and we don't need to use the stencil buffer to
     set the clip. We keep the entry as a rect entry rather than a
     window rect entry so that it will be easier to detect if the
     modelview matrix is that same as when a rectangle is added to the
     journal. In that case we can use the original clip coordinates
     and modify the rectangle instead. */
  gboolean               can_be_scissor;

  /* The matrix that was current when the clip was set */
  CoglMatrix             matrix;
};

struct _CoglClipStackWindowRect
{
  CoglClipStack     _parent_data;

  /* The window rect clip doesn't need any specific data because it
     just adds to the scissor clip */
};

struct _CoglClipStackPath
{
  CoglClipStack     _parent_data;

  /* The matrix that was current when the clip was set */
  CoglMatrix             matrix;

  CoglPath              *path;
};

CoglClipStack *
_cogl_clip_stack_push_window_rectangle (CoglClipStack *stack,
                                        int x_offset,
                                        int y_offset,
                                        int width,
                                        int height);

CoglClipStack *
_cogl_clip_stack_push_rectangle (CoglClipStack *stack,
                                 float x_1,
                                 float y_1,
                                 float x_2,
                                 float y_2,
                                 const CoglMatrix *modelview_matrix);

CoglClipStack *
_cogl_clip_stack_push_from_path (CoglClipStack *stack,
                                 CoglPath *path,
                                 const CoglMatrix *modelview_matrix);
CoglClipStack *
_cogl_clip_stack_pop (CoglClipStack *stack);

void
_cogl_clip_stack_flush (CoglClipStack *stack);

CoglClipStack *
_cogl_clip_stack_ref (CoglClipStack *stack);

void
_cogl_clip_stack_unref (CoglClipStack *stack);

void
_cogl_clip_stack_dirty (void);

#endif /* __COGL_CLIP_STACK_H */