use high on painting shaders

data/shaders/texture-alpha-sep.glsl

@@ -17,17 +17,17 @@ void main()
 uniform sampler2D tex;
 uniform sampler2D tex_alpha;
 uniform sampler2D tex_bg;
-uniform mediump float alpha;
+uniform highp float alpha;
 uniform bool highlight;
 
-in mediump vec2 uv;
-out mediump vec4 frag;
+in highp vec2 uv;
+out highp vec4 frag;
 
 void main()
 {
-    mediump vec3 rgb = texture(tex, uv).rgb;
-    mediump float a = texture(tex_alpha, uv).a;
-    mediump vec4 c = vec4(rgb, a);
+    highp vec3 rgb = texture(tex, uv).rgb;
+    highp float a = texture(tex_alpha, uv).a;
+    highp vec4 c = vec4(rgb, a);
     frag = highlight ? 
         vec4(clamp(vec3(0.3) + c.rgb, vec3(0.0), vec3(1.0)), c.a) : 
         texture(tex, uv) * vec4(1.0, 1.0, 1.0, alpha);