Shaders: make GLSL code for fullscreen triangle reusable.

Now you can just add the file and call `fullScreenTriangle()`.

src/Shaders/FullScreenTriangle.glsl

@@ -0,0 +1,36 @@
+/*
+    This file is part of Magnum.
+
+    Copyright © 2010, 2011, 2012, 2013 Vladimír Vondruš <mosra@centrum.cz>
+
+    Permission is hereby granted, free of charge, to any person obtaining a
+    copy of this software and associated documentation files (the "Software"),
+    to deal in the Software without restriction, including without limitation
+    the rights to use, copy, modify, merge, publish, distribute, sublicense,
+    and/or sell copies of the Software, and to permit persons to whom the
+    Software is furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included
+    in all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+    DEALINGS IN THE SOFTWARE.
+*/
+
+#ifndef NEW_GLSL
+attribute lowp vec4 position;
+#endif
+
+void fullScreenTriangle() {
+    #ifdef NEW_GLSL
+    gl_Position = vec4((gl_VertexID == 2) ?  3.0 : -1.0,
+                       (gl_VertexID == 1) ? -3.0 :  1.0, 0.0, 1.0);
+    #else
+    gl_Position = position;
+    #endif
+}

src/Shaders/resources.conf

@@ -15,6 +15,9 @@ filename=Flat3D.vert
 [file]
 filename=Flat.frag
 
+[file]
+filename=FullScreenTriangle.glsl
+
 [file]
 filename=MeshVisualizer.vert
 

src/TextureTools/DistanceField.cpp

@@ -79,6 +79,7 @@ DistanceFieldShader::DistanceFieldShader(): radiusUniform(0), scalingUniform(1)
 
     Shader vert(v, Shader::Type::Vertex);
     vert.addSource(rs.get("compatibility.glsl"))
+        .addSource(rs.get("FullScreenTriangle.glsl"))
         .addSource(rs.get("DistanceFieldShader.vert"));
     CORRADE_INTERNAL_ASSERT_OUTPUT(vert.compile());
     attachShader(vert);

src/TextureTools/DistanceFieldShader.vert

@@ -22,15 +22,6 @@
     DEALINGS IN THE SOFTWARE.
 */
 
-#ifndef NEW_GLSL
-attribute lowp vec4 position;
-#endif
-
 void main() {
-    #ifdef NEW_GLSL
-    gl_Position = vec4((gl_VertexID == 2) ?  3.0 : -1.0,
-                       (gl_VertexID == 1) ? -3.0 :  1.0, 0.0, 1.0);
-    #else
-    gl_Position = position;
-    #endif
+    fullScreenTriangle();
 }

src/TextureTools/resources.conf

@@ -1,5 +1,9 @@
 group=MagnumTextureTools
 
+[file]
+filename=../Shaders/FullScreenTriangle.glsl
+alias=FullScreenTriangle.glsl
+
 [file]
 filename=DistanceFieldShader.vert