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mutter/cogl/cogl-clip-stack.c
Robert Bragg 0ec9e406ea clip-stack: combine modelview-projection in set_clip_planes 
When using clip planes and we we have to project some vertices into
screen coordinates we used to transform those by the modelview and then
the projection matrix separately. Now we combine the modelview and
projection matrix and then use that to transform the vertices in one
step instead.
2010-11-23 12:50:29 +00:00

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/*
* 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/>.
*
*
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <string.h>
#include <math.h>
#include <glib.h>
#include "cogl.h"
#include "cogl-clip-stack.h"
#include "cogl-primitives.h"
#include "cogl-context.h"
#include "cogl-internal.h"
#include "cogl-framebuffer-private.h"
#include "cogl-journal-private.h"
#include "cogl-util.h"
#include "cogl-path-private.h"
#include "cogl-matrix-private.h"
#include "cogl-primitives-private.h"
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;
/* 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;
};
static void
project_vertex (const CoglMatrix *modelview_projection,
float *vertex)
{
int i;
cogl_matrix_transform_point (modelview_projection,
&vertex[0], &vertex[1],
&vertex[2], &vertex[3]);
/* Convert from homogenized coordinates */
for (i = 0; i < 4; i++)
vertex[i] /= vertex[3];
}
static void
set_clip_plane (GLint plane_num,
const float *vertex_a,
const float *vertex_b)
{
#if defined (HAVE_COGL_GLES2) || defined (HAVE_COGL_GLES)
GLfloat plane[4];
#else
GLdouble plane[4];
#endif
GLfloat angle;
CoglFramebuffer *framebuffer = _cogl_get_framebuffer ();
CoglMatrixStack *modelview_stack =
_cogl_framebuffer_get_modelview_stack (framebuffer);
CoglMatrixStack *projection_stack =
_cogl_framebuffer_get_projection_stack (framebuffer);
CoglMatrix inverse_projection;
_COGL_GET_CONTEXT (ctx, NO_RETVAL);
_cogl_matrix_stack_get_inverse (projection_stack, &inverse_projection);
/* Calculate the angle between the axes and the line crossing the
two points */
angle = atan2f (vertex_b[1] - vertex_a[1],
vertex_b[0] - vertex_a[0]) * (180.0/G_PI);
_cogl_matrix_stack_push (modelview_stack);
/* Load the inverse of the projection matrix so we can specify the plane
* in screen coordinates */
_cogl_matrix_stack_set (modelview_stack, &inverse_projection);
/* Rotate about point a */
_cogl_matrix_stack_translate (modelview_stack,
vertex_a[0], vertex_a[1], vertex_a[2]);
/* Rotate the plane by the calculated angle so that it will connect
the two points */
_cogl_matrix_stack_rotate (modelview_stack, angle, 0.0f, 0.0f, 1.0f);
_cogl_matrix_stack_translate (modelview_stack,
-vertex_a[0], -vertex_a[1], -vertex_a[2]);
_cogl_matrix_stack_flush_to_gl (modelview_stack, COGL_MATRIX_MODELVIEW);
plane[0] = 0;
plane[1] = -1.0;
plane[2] = 0;
plane[3] = vertex_a[1];
#if defined (HAVE_COGL_GLES2) || defined (HAVE_COGL_GLES)
GE( glClipPlanef (plane_num, plane) );
#else
GE( glClipPlane (plane_num, plane) );
#endif
_cogl_matrix_stack_pop (modelview_stack);
}
static void
set_clip_planes (float x_1,
float y_1,
float x_2,
float y_2)
{
CoglFramebuffer *framebuffer = _cogl_get_framebuffer ();
CoglMatrixStack *modelview_stack =
_cogl_framebuffer_get_modelview_stack (framebuffer);
CoglMatrix modelview_matrix;
CoglMatrixStack *projection_stack =
_cogl_framebuffer_get_projection_stack (framebuffer);
CoglMatrix projection_matrix;
CoglMatrix modelview_projection;
float signed_area;
float vertex_tl[4] = { x_1, y_1, 0, 1.0 };
float vertex_tr[4] = { x_2, y_1, 0, 1.0 };
float vertex_bl[4] = { x_1, y_2, 0, 1.0 };
float vertex_br[4] = { x_2, y_2, 0, 1.0 };
_cogl_matrix_stack_get (projection_stack, &projection_matrix);
_cogl_matrix_stack_get (modelview_stack, &modelview_matrix);
cogl_matrix_multiply (&modelview_projection,
&projection_matrix,
&modelview_matrix);
project_vertex (&modelview_projection, vertex_tl);
project_vertex (&modelview_projection, vertex_tr);
project_vertex (&modelview_projection, vertex_bl);
project_vertex (&modelview_projection, vertex_br);
/* Calculate the signed area of the polygon formed by the four
vertices so that we can know its orientation */
signed_area = (vertex_tl[0] * (vertex_tr[1] - vertex_bl[1])
+ vertex_tr[0] * (vertex_br[1] - vertex_tl[1])
+ vertex_br[0] * (vertex_bl[1] - vertex_tr[1])
+ vertex_bl[0] * (vertex_tl[1] - vertex_br[1]));
/* Set the clip planes to form lines between all of the vertices
using the same orientation as we calculated */
if (signed_area > 0.0f)
{
/* counter-clockwise */
set_clip_plane (GL_CLIP_PLANE0, vertex_tl, vertex_bl);
set_clip_plane (GL_CLIP_PLANE1, vertex_bl, vertex_br);
set_clip_plane (GL_CLIP_PLANE2, vertex_br, vertex_tr);
set_clip_plane (GL_CLIP_PLANE3, vertex_tr, vertex_tl);
}
else
{
/* clockwise */
set_clip_plane (GL_CLIP_PLANE0, vertex_tl, vertex_tr);
set_clip_plane (GL_CLIP_PLANE1, vertex_tr, vertex_br);
set_clip_plane (GL_CLIP_PLANE2, vertex_br, vertex_bl);
set_clip_plane (GL_CLIP_PLANE3, vertex_bl, vertex_tl);
}
}
static void
add_stencil_clip_rectangle (float x_1,
float y_1,
float x_2,
float y_2,
gboolean first)
{
CoglFramebuffer *framebuffer = _cogl_get_framebuffer ();
CoglMatrixStack *modelview_stack =
_cogl_framebuffer_get_modelview_stack (framebuffer);
CoglMatrixStack *projection_stack =
_cogl_framebuffer_get_projection_stack (framebuffer);
_COGL_GET_CONTEXT (ctx, NO_RETVAL);
/* temporarily swap in our special stenciling pipeline */
cogl_push_source (ctx->stencil_pipeline);
if (first)
{
GE( glEnable (GL_STENCIL_TEST) );
/* Initially disallow everything */
GE( glClearStencil (0) );
GE( glClear (GL_STENCIL_BUFFER_BIT) );
/* Punch out a hole to allow the rectangle */
GE( glStencilFunc (GL_NEVER, 0x1, 0x1) );
GE( glStencilOp (GL_REPLACE, GL_REPLACE, GL_REPLACE) );
/* This can be called from the journal code which doesn't flush
the matrix stacks between calls so we need to ensure they're
flushed now */
_cogl_matrix_stack_flush_to_gl (modelview_stack,
COGL_MATRIX_MODELVIEW);
_cogl_matrix_stack_flush_to_gl (projection_stack,
COGL_MATRIX_PROJECTION);
_cogl_rectangle_immediate (x_1, y_1, x_2, y_2);
}
else
{
/* Add one to every pixel of the stencil buffer in the
rectangle */
GE( glStencilFunc (GL_NEVER, 0x1, 0x3) );
GE( glStencilOp (GL_INCR, GL_INCR, GL_INCR) );
_cogl_rectangle_immediate (x_1, y_1, x_2, y_2);
/* Subtract one from all pixels in the stencil buffer so that
only pixels where both the original stencil buffer and the
rectangle are set will be valid */
GE( glStencilOp (GL_DECR, GL_DECR, GL_DECR) );
_cogl_matrix_stack_push (projection_stack);
_cogl_matrix_stack_load_identity (projection_stack);
_cogl_matrix_stack_push (modelview_stack);
_cogl_matrix_stack_load_identity (modelview_stack);
_cogl_matrix_stack_flush_to_gl (modelview_stack,
COGL_MATRIX_MODELVIEW);
_cogl_matrix_stack_flush_to_gl (projection_stack,
COGL_MATRIX_PROJECTION);
_cogl_rectangle_immediate (-1.0, -1.0, 1.0, 1.0);
_cogl_matrix_stack_pop (modelview_stack);
_cogl_matrix_stack_pop (projection_stack);
}
/* Restore the stencil mode */
GE( glStencilFunc (GL_EQUAL, 0x1, 0x1) );
GE( glStencilOp (GL_KEEP, GL_KEEP, GL_KEEP) );
/* restore the original source pipeline */
cogl_pop_source ();
}
static void
disable_stencil_buffer (void)
{
GE( glDisable (GL_STENCIL_TEST) );
}
static void
enable_clip_planes (void)
{
GE( glEnable (GL_CLIP_PLANE0) );
GE( glEnable (GL_CLIP_PLANE1) );
GE( glEnable (GL_CLIP_PLANE2) );
GE( glEnable (GL_CLIP_PLANE3) );
}
static void
disable_clip_planes (void)
{
GE( glDisable (GL_CLIP_PLANE3) );
GE( glDisable (GL_CLIP_PLANE2) );
GE( glDisable (GL_CLIP_PLANE1) );
GE( glDisable (GL_CLIP_PLANE0) );
}
static gpointer
_cogl_clip_stack_push_entry (CoglClipStack *clip_stack,
size_t size,
CoglClipStackType type)
{
CoglClipStack *entry = g_slice_alloc (size);
/* The new entry starts with a ref count of 1 because the stack
holds a reference to it as it is the top entry */
entry->ref_count = 1;
entry->type = type;
entry->parent = clip_stack;
/* We don't need to take a reference to the parent from the entry
because the we are stealing the ref in the new stack top */
return entry;
}
/* Sets the window-space bounds of the entry based on the projected
coordinates of the given rectangle */
static void
_cogl_clip_stack_entry_set_bounds (CoglClipStack *entry,
float x_1,
float y_1,
float x_2,
float y_2,
const CoglMatrix *modelview)
{
CoglMatrix projection;
float viewport[4];
float verts[4 * 2] = { x_1, y_1, x_2, y_1, x_2, y_2, x_1, y_2 };
float min_x = G_MAXFLOAT, min_y = G_MAXFLOAT;
float max_x = -G_MAXFLOAT, max_y = -G_MAXFLOAT;
int i;
cogl_get_projection_matrix (&projection);
cogl_get_viewport (viewport);
for (i = 0; i < 4; i++)
{
float *v = verts + i * 2;
/* Project the coordinates to window space coordinates */
_cogl_transform_point (modelview, &projection, viewport, v, v + 1);
if (v[0] > max_x)
max_x = v[0];
if (v[0] < min_x)
min_x = v[0];
if (v[1] > max_y)
max_y = v[1];
if (v[1] < min_y)
min_y = v[1];
}
entry->bounds_x0 = floorf (min_x);
entry->bounds_x1 = ceilf (max_x);
entry->bounds_y0 = floorf (min_y);
entry->bounds_y1 = ceilf (max_y);
}
CoglClipStack *
_cogl_clip_stack_push_window_rectangle (CoglClipStack *stack,
int x_offset,
int y_offset,
int width,
int height)
{
CoglClipStack *entry;
entry = _cogl_clip_stack_push_entry (stack,
sizeof (CoglClipStackWindowRect),
COGL_CLIP_STACK_WINDOW_RECT);
entry->bounds_x0 = x_offset;
entry->bounds_x1 = x_offset + width;
entry->bounds_y0 = y_offset;
entry->bounds_y1 = y_offset + height;
return entry;
}
CoglClipStack *
_cogl_clip_stack_push_rectangle (CoglClipStack *stack,
float x_1,
float y_1,
float x_2,
float y_2,
const CoglMatrix *modelview_matrix)
{
CoglClipStackRect *entry;
/* Make a new entry */
entry = _cogl_clip_stack_push_entry (stack,
sizeof (CoglClipStackRect),
COGL_CLIP_STACK_RECT);
entry->x0 = x_1;
entry->y0 = y_1;
entry->x1 = x_2;
entry->y1 = y_2;
entry->matrix = *modelview_matrix;
_cogl_clip_stack_entry_set_bounds ((CoglClipStack *) entry,
x_1, y_1, x_2, y_2, modelview_matrix);
return (CoglClipStack *) entry;
}
CoglClipStack *
_cogl_clip_stack_push_from_path (CoglClipStack *stack,
CoglPath *path,
const CoglMatrix *modelview_matrix)
{
CoglClipStackPath *entry;
float x_1, y_1, x_2, y_2;
entry = _cogl_clip_stack_push_entry (stack,
sizeof (CoglClipStackPath),
COGL_CLIP_STACK_PATH);
entry->path = cogl_path_copy (path);
entry->matrix = *modelview_matrix;
_cogl_path_get_bounds (path, &x_1, &y_1, &x_2, &y_2);
_cogl_clip_stack_entry_set_bounds ((CoglClipStack *) entry,
x_1, y_1, x_2, y_2, modelview_matrix);
return (CoglClipStack *) entry;
}
CoglClipStack *
_cogl_clip_stack_ref (CoglClipStack *entry)
{
/* A NULL pointer is considered a valid stack so we should accept
that as an argument */
if (entry)
entry->ref_count++;
return entry;
}
void
_cogl_clip_stack_unref (CoglClipStack *entry)
{
/* Unref all of the entries until we hit the root of the list or the
entry still has a remaining reference */
while (entry && --entry->ref_count <= 0)
{
CoglClipStack *parent = entry->parent;
switch (entry->type)
{
case COGL_CLIP_STACK_RECT:
g_slice_free1 (sizeof (CoglClipStackRect), entry);
break;
case COGL_CLIP_STACK_WINDOW_RECT:
g_slice_free1 (sizeof (CoglClipStackWindowRect), entry);
break;
case COGL_CLIP_STACK_PATH:
cogl_object_unref (((CoglClipStackPath *) entry)->path);
g_slice_free1 (sizeof (CoglClipStackPath), entry);
break;
default:
g_assert_not_reached ();
}
entry = parent;
}
}
CoglClipStack *
_cogl_clip_stack_pop (CoglClipStack *stack)
{
CoglClipStack *new_top;
g_return_val_if_fail (stack != NULL, NULL);
/* To pop we are moving the top of the stack to the old top's parent
node. The stack always needs to have a reference to the top entry
so we must take a reference to the new top. The stack would have
previously had a reference to the old top so we need to decrease
the ref count on that. We need to ref the new head first in case
this stack was the only thing referencing the old top. In that
case the call to _cogl_clip_stack_entry_unref will unref the
parent. */
new_top = stack->parent;
_cogl_clip_stack_ref (new_top);
_cogl_clip_stack_unref (stack);
return new_top;
}
void
_cogl_clip_stack_flush (CoglClipStack *stack)
{
int has_clip_planes;
gboolean using_clip_planes = FALSE;
gboolean using_stencil_buffer = FALSE;
int scissor_x0 = 0;
int scissor_y0 = 0;
int scissor_x1 = G_MAXINT;
int scissor_y1 = G_MAXINT;
CoglMatrixStack *modelview_stack;
CoglClipStack *entry;
int scissor_y_start;
_COGL_GET_CONTEXT (ctx, NO_RETVAL);
/* If we have already flushed this state then we don't need to do
anything */
if (ctx->current_clip_stack_valid)
{
if (ctx->current_clip_stack == stack)
return;
_cogl_clip_stack_unref (ctx->current_clip_stack);
}
ctx->current_clip_stack_valid = TRUE;
ctx->current_clip_stack = _cogl_clip_stack_ref (stack);
modelview_stack =
_cogl_framebuffer_get_modelview_stack (_cogl_get_framebuffer ());
has_clip_planes = cogl_features_available (COGL_FEATURE_FOUR_CLIP_PLANES);
if (has_clip_planes)
disable_clip_planes ();
disable_stencil_buffer ();
/* If the stack is empty then there's nothing else to do */
if (stack == NULL)
{
ctx->current_clip_stack_uses_stencil = FALSE;
GE (glDisable (GL_SCISSOR_TEST));
return;
}
/* Calculate the scissor rect first so that if we eventually have to
clear the stencil buffer then the clear will be clipped to the
intersection of all of the bounding boxes. This saves having to
clear the whole stencil buffer */
for (entry = stack; entry; entry = entry->parent)
{
/* Get the intersection of the current scissor and the bounding
box of this clip */
scissor_x0 = MAX (scissor_x0, entry->bounds_x0);
scissor_y0 = MAX (scissor_y0, entry->bounds_y0);
scissor_x1 = MIN (scissor_x1, entry->bounds_x1);
scissor_y1 = MIN (scissor_y1, entry->bounds_y1);
}
/* Enable scissoring as soon as possible */
if (scissor_x0 >= scissor_x1 || scissor_y0 >= scissor_y1)
scissor_x0 = scissor_y0 = scissor_x1 = scissor_y1 = scissor_y_start = 0;
else
{
CoglFramebuffer *framebuffer = _cogl_get_framebuffer ();
/* We store the entry coordinates in Cogl coordinate space
* but OpenGL requires the window origin to be the bottom
* left so we may need to convert the incoming coordinates.
*
* NB: Cogl forces all offscreen rendering to be done upside
* down so in this case no conversion is needed.
*/
if (cogl_is_offscreen (framebuffer))
scissor_y_start = scissor_y0;
else
{
int framebuffer_height =
_cogl_framebuffer_get_height (framebuffer);
scissor_y_start = framebuffer_height - scissor_y1;
}
}
GE (glEnable (GL_SCISSOR_TEST));
GE (glScissor (scissor_x0, scissor_y_start,
scissor_x1 - scissor_x0,
scissor_y1 - scissor_y0));
/* Add all of the entries. This will end up adding them in the
reverse order that they were specified but as all of the clips
are intersecting it should work out the same regardless of the
order */
for (entry = stack; entry; entry = entry->parent)
{
if (entry->type == COGL_CLIP_STACK_PATH)
{
CoglClipStackPath *path_entry = (CoglClipStackPath *) entry;
_cogl_matrix_stack_push (modelview_stack);
_cogl_matrix_stack_set (modelview_stack, &path_entry->matrix);
_cogl_add_path_to_stencil_buffer (path_entry->path,
using_stencil_buffer,
TRUE);
_cogl_matrix_stack_pop (modelview_stack);
using_stencil_buffer = TRUE;
}
else if (entry->type == COGL_CLIP_STACK_RECT)
{
CoglClipStackRect *rect = (CoglClipStackRect *) entry;
_cogl_matrix_stack_push (modelview_stack);
_cogl_matrix_stack_set (modelview_stack, &rect->matrix);
/* If we support clip planes and we haven't already used
them then use that instead */
if (has_clip_planes)
{
set_clip_planes (rect->x0,
rect->y0,
rect->x1,
rect->y1);
using_clip_planes = TRUE;
/* We can't use clip planes a second time */
has_clip_planes = FALSE;
}
else
{
add_stencil_clip_rectangle (rect->x0,
rect->y0,
rect->x1,
rect->y1,
!using_stencil_buffer);
using_stencil_buffer = TRUE;
}
_cogl_matrix_stack_pop (modelview_stack);
}
/* We don't need to do anything for window space rectangles
because their functionality is entirely implemented by the
entry bounding box */
}
/* Enabling clip planes is delayed to now so that they won't affect
setting up the stencil buffer */
if (using_clip_planes)
enable_clip_planes ();
ctx->current_clip_stack_uses_stencil = using_stencil_buffer;
}
void
_cogl_clip_stack_dirty (void)
{
_COGL_GET_CONTEXT (ctx, NO_RETVAL);
if (ctx->current_clip_stack_valid)
{
ctx->current_clip_stack_valid = FALSE;
_cogl_clip_stack_unref (ctx->current_clip_stack);
}
}
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