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| author | Filippo Argiolas <filippo.argiolas@gmail.com> | 2010-04-24 21:11:35 +0200 |
|---|---|---|
| committer | Filippo Argiolas <filippo.argiolas@gmail.com> | 2010-04-24 21:11:35 +0200 |
| commit | 71d90751ea9c94650953659008fb5282acce52cd (patch) | |
| tree | 30c8b81d76736c56b7030c4e02e43152cc9d7a86 | |
| parent | bce3332d94ad13d1b0ac06de208811b176c3c94b (diff) | |
twirl: get rid of polar coordinates conversion
Get rid of polar coordinates in the twirl effect. The same can be done
using a rotation matrix, saving alu instructions and, most of all,
avoiding the use of the evil atan() function (which uses IF operators).
Calculate rotation angle in a saner, understandable way.
Works on i915! (Hope it still works elsewhere too as I'm not able to
test at the moment)
| -rw-r--r-- | gst/gl/effects/gstgleffectssources.c | 14 |
1 files changed, 9 insertions, 5 deletions
diff --git a/gst/gl/effects/gstgleffectssources.c b/gst/gl/effects/gstgleffectssources.c index a334fad..c723582 100644 --- a/gst/gl/effects/gstgleffectssources.c +++ b/gst/gl/effects/gstgleffectssources.c @@ -209,11 +209,15 @@ const gchar *twirl_fragment_source = " vec2 texturecoord = gl_TexCoord[0].xy;" " vec2 normcoord;" " normcoord = texturecoord / tex_size - 1.0;" - " float r = length (normcoord);" - " float phi = atan (normcoord.y, normcoord.x);" - " phi += (1.0 - smoothstep (-0.6, 0.6, r)) * 4.8;" - " normcoord.x = r * cos(phi);" - " normcoord.y = r * sin(phi);" + " float r = length (normcoord);" + /* calculate rotation angle: maximum (about pi/2) at the origin and + * gradually decrease it up to 0.6 of each quadrant */ + " float phi = (1.0 - smoothstep (0.0, 0.6, r)) * 1.6;" + /* precalculate sin phi and cos phi, save some alu */ + " float s = sin(phi);" + " float c = cos(phi);" + /* rotate */ + " normcoord *= mat2(c, s, -s, c);" " texturecoord = (normcoord + 1.0) * tex_size;" " vec4 color = texture2DRect (tex, texturecoord); " " gl_FragColor = color;" |