Fix untextured cube caps with GLSL

effects/cube/cube.cpp

@@ -770,6 +770,7 @@ void CubeEffect::paintCap(bool frontFirst, float zOffset)
             m_capShader->setUniform("screenTransformation", m_rotationMatrix);
         }
         m_capShader->setUniform("windowTransformation", capMatrix);
+        m_capShader->setUniform("u_untextured", texturedCaps ? 0 : 1);
         if (texturedCaps && effects->numberOfDesktops() > 3 && capTexture) {
             capTexture->bind();
         }

effects/cube/data/cube-cap.glsl

@@ -2,6 +2,7 @@ uniform sampler2D sampler;
 uniform vec4 u_capColor;
 uniform float u_opacity;
 uniform int u_mirror;
+uniform int u_untextured;
 
 varying vec2 varyingTexCoords;
 
@@ -18,7 +19,7 @@ void main() {
     vec2 texCoord = mirrorTex(varyingTexCoords);
     vec4 tex = texture2D(sampler, texCoord);
     if (texCoord.s < 0.0 || texCoord.s > 1.0 ||
-            texCoord.t < 0.0 || texCoord.t > 1.0) {
+            texCoord.t < 0.0 || texCoord.t > 1.0 || u_untextured != 0) {
         tex = u_capColor;
     }
     color.rgb = tex.rgb*tex.a + color.rgb*(1.0-tex.a);