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[texture] fix rounding when calculating update_fbo viewport offset

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When rendering to an fbo for supporting clutter_texture_new_from_actor we
render to an fbo with the same size as the source actor, but with a viewport
the same size as the stage.  We offset the viewport so when we render the
source actor in its normal transformed stage position it lands on the fbo.
Previously we were rounding the transformed position given as a float by
truncating the fraction (just using a C cast) but that resulted in an
incorrect pixel offset when rendering offscreen depending on the source
position.

We now simply + 0.5 before casting (or -0.5 for negative numbers)
This commit is contained in:
Robert Bragg 2009-11-01 23:56:03 +00:00
parent 309f852efb
commit ae57c30e93
1 changed files with 13 additions and 1 deletions
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14
clutter/clutter-texture.c
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@ -455,6 +455,7 @@ set_viewport_with_buffer_under_fbo_source (ClutterActor *fbo_source,
{
ClutterVertex verts[4];
float x_min = G_MAXFLOAT, y_min = G_MAXFLOAT;
int x_offset, y_offset;
int i;
/* Get the actors allocation transformed into screen coordinates.
@ -472,9 +473,19 @@ set_viewport_with_buffer_under_fbo_source (ClutterActor *fbo_source,
y_min = verts[i].y;
}
/* XXX: It's not good enough to round by simply truncating the fraction here
* via a cast, as it results in offscreen rendering being offset by 1 pixel
* in many cases... */
#define ROUND(x) ((x) >= 0 ? (long)((x) + 0.5) : (long)((x) - 0.5))
x_offset = ROUND (-x_min);
y_offset = ROUND (-y_min);
#undef ROUND
/* 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);
cogl_set_viewport (x_offset, y_offset, viewport_width, viewport_height);
}
static void
@ -543,6 +554,7 @@ update_fbo (ClutterActor *self)
NULL);
}
/* cogl_clear is called to clear the buffers */
cogl_color_set_from_4ub (&transparent_col, 0, 0, 0, 0);
cogl_clear (&transparent_col,