Copy distance field shader changes to OpenGL runtime

Also fixes the OpenGL runtime to use alpha channel for the glyph texture
when using ES2.

Task-number: QT3DS-3343
Change-Id: Ia37c341802e504da21ebeaff6f3f1f5b50bd1bfe
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>
Reviewed-by: Antti Määttä <antti.maatta@qt.io>
 

1 files changed, 20 insertions, 4 deletions

diff --git a/src/Runtime/res/effectlib/distancefieldtext.frag b/src/Runtime/res/effectlib/distancefieldtext.frag
index efcf89e4..1d834902 100644
--- a/src/Runtime/res/effectlib/distancefieldtext.frag
+++ b/src/Runtime/res/effectlib/distancefieldtext.frag
@@ -1,12 +1,28 @@
+#ifdef GL_OES_standard_derivatives
+#  extension GL_OES_standard_derivatives : enable
+#else
+#  define use_fallback
+#endif
+
 varying highp vec2 sampleCoord;
-varying highp vec2 alphas;
 
 uniform sampler2D _qt_texture;
 uniform highp vec4 color;
 
+#ifdef use_fallback
+varying highp vec2 alphas;
+#endif
+
 void main()
 {
-    gl_FragColor = color * smoothstep(alphas.x,
-                                      alphas.y,
-                                      texture2D(_qt_texture, sampleCoord).a);
+    highp float distance = texture2D(_qt_texture, sampleCoord).a;
+
+#ifdef use_fallback
+    highp float alpha = smoothstep(alphas.x, alphas.y, distance);
+#else
+    highp float f = fwidth(distance);
+    highp float alpha = smoothstep(0.5 - f, 0.5, distance);
+#endif
+
+    gl_FragColor = color * alpha;
 }