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[texture] switch to a new design for handling offscreen rendering

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For supporting clutter_texture_new_from_actor(): when updating a
ClutterTexture's fbo we previously set up an offset frustum in the
perspective matrix before rendering source actors to an offscreen draw
buffer so as to give a perspective as if it were being drawn at its
original stage location.

Now that Cogl supports offset viewports there is a simpler way...

When we come to render the source actor to our offscreen draw buffer we
now copy the projection matrix from the stage; we create a viewport
that's also the same size as the stage (though larger than the offscreen
draw buffer) and as before we apply the modelview transformations of
the source actors ancestry before painting it.

The only trick we need now is to offset the viewport according to the
transformed (to screen space) allocation of the source actor (something we
required previously too).  We negatively offset the stage sized viewport
such that the smaller offscreen draw buffer is positioned to sit underneath
the source actor in stage coordinates.
This commit is contained in:
Robert Bragg 2009-11-02 01:14:50 +00:00
parent 94a6028358
commit 309f852efb
1 changed files with 35 additions and 65 deletions
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100
clutter/clutter-texture.c
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@ -449,66 +449,32 @@ clutter_texture_allocate (ClutterActor *self,
}
static void
clutter_texture_set_fbo_projection (ClutterActor *self)
set_viewport_with_buffer_under_fbo_source (ClutterActor *fbo_source,
int viewport_width,
int viewport_height)
{
ClutterTexturePrivate *priv = CLUTTER_TEXTURE (self)->priv;
ClutterVertex verts[4];
gfloat viewport[4];
gfloat x_min, x_max, y_min, y_max;
gfloat tx_min, tx_max, ty_min, ty_max;
gfloat tan_angle, near_size;
ClutterPerspective perspective;
ClutterStage *stage;
float x_min = G_MAXFLOAT, y_min = G_MAXFLOAT;
int i;
/* Get the bounding rectangle of the source as drawn in screen
coordinates */
clutter_actor_get_abs_allocation_vertices (priv->fbo_source, verts);
/* Get the actors allocation transformed into screen coordinates.
*
* XXX: Note: this may not be a bounding box for the actor, since an
* actor with depth may escape the box due to its perspective
* projection. */
clutter_actor_get_abs_allocation_vertices (fbo_source, verts);
x_min = x_max = verts[0].x;
y_min = y_max = verts[0].y;
for (i = 1; i < G_N_ELEMENTS (verts); ++i)
for (i = 0; i < G_N_ELEMENTS (verts); ++i)
{
if (verts[i].x < x_min)
x_min = verts[i].x;
if (verts[i].x > x_max)
x_max = verts[i].x;
if (verts[i].y < y_min)
y_min = verts[i].y;
if (verts[i].y > y_max)
y_max = verts[i].y;
}
stage = CLUTTER_STAGE (clutter_actor_get_stage (self));
clutter_stage_get_perspective (stage, &perspective);
/* Convert the coordinates back to [-1,1] range */
cogl_get_viewport (viewport);
tx_min = (x_min / viewport[2])
* 2 - 1.0;
tx_max = (x_max / viewport[2])
* 2 - 1.0;
ty_min = (y_min / viewport[3])
* 2 - 1.0;
ty_max = (y_max / viewport[3])
* 2 - 1.0;
/* Set up a projection matrix so that the actor will be projected as
if it was drawn at its original location */
tan_angle = tanf ((perspective.fovy / 2) * (G_PI / 180.0));
near_size = perspective.z_near * tan_angle;
cogl_frustum ((tx_min * near_size),
(tx_max * near_size),
(-ty_min * near_size),
(-ty_max * near_size),
perspective.z_near,
perspective.z_far);
/* translate the viewport so that the source actor lands on the
* sub-region backed by the offscreen draw buffer... */
cogl_set_viewport (-x_min, -y_min, viewport_width, viewport_height);
}
static void
@ -527,8 +493,8 @@ update_fbo (ClutterActor *self)
if (context->shaders)
shader = clutter_actor_get_shader (context->shaders->data);
/* Temporarily turn of the shader on the top of the context's
* shader stack, to restore the GL pipeline to it's natural state.
/* Temporarily turn off the shader on the top of the context's shader stack,
* to restore the GL pipeline to it's natural state.
*/
if (shader)
clutter_shader_set_is_enabled (shader, FALSE);
@ -542,23 +508,34 @@ update_fbo (ClutterActor *self)
gfloat stage_width, stage_height;
ClutterActor *source_parent;
/* We copy the projection and modelview matrices from the stage to
* the offscreen draw buffer and create a viewport larger than the
* offscreen draw buffer - the same size as the stage.
*
* The fbo source actor gets rendered into this stage size viewport at the
* same position it normally would after applying all it's usual parent
* transforms and it's own scale and rotate transforms etc.
*
* The viewport is offset such that the offscreen buffer will be positioned
* under the actor.
*/
clutter_stage_get_perspective (CLUTTER_STAGE (stage), &perspective);
clutter_actor_get_size (stage, &stage_width, &stage_height);
/* Use below to set the modelview matrix as if the viewport
was still the same size as the stage */
/* Set the projection matrix modelview matrix and viewport size as
* they are for the stage... */
_cogl_setup_viewport (stage_width, stage_height,
perspective.fovy,
perspective.aspect,
perspective.z_near,
perspective.z_far);
/* Use a projection matrix that makes the actor appear as it
would if it was rendered at its normal screen location */
clutter_texture_set_fbo_projection (self);
/* Reset the viewport to the size of the FBO */
cogl_set_viewport (0, 0, priv->image_width, priv->image_height);
/* Negatively offset the viewport so that the offscreen draw buffer is
* position underneath the fbo_source actor... */
set_viewport_with_buffer_under_fbo_source (priv->fbo_source,
stage_width,
stage_height);
/* Reapply the source's parent transformations */
if ((source_parent = clutter_actor_get_parent (priv->fbo_source)))
@ -579,13 +556,6 @@ update_fbo (ClutterActor *self)
/* Restore drawing to the previous draw buffer */
cogl_pop_draw_buffer ();
/* Restore the perspective matrix using cogl_perspective so that
the inverse matrix will be right */
cogl_perspective (perspective.fovy,
perspective.aspect,
perspective.z_near,
perspective.z_far);
/* If there is a shader on top of the shader stack, turn it back on. */
if (shader)
clutter_shader_set_is_enabled (shader, TRUE);