PhongShader: fall back to GLSL 1.20 if 3.30/3.20 is not supported.

src/Shaders/PhongShader.cpp

@@ -17,14 +17,21 @@
 
 #include <Utility/Resource.h>
 
+#include "Extensions.h"
 #include "Shader.h"
 
 namespace Magnum { namespace Shaders {
 
 PhongShader::PhongShader() {
     Corrade::Utility::Resource rs("MagnumShaders");
-    attachShader(Shader::fromData(Version::GL330, Shader::Type::Vertex, rs.get("PhongShader.vert")));
-    attachShader(Shader::fromData(Version::GL330, Shader::Type::Fragment, rs.get("PhongShader.frag")));
+    Version v = Context::current()->isVersionSupported(Version::GL320) ? Version::GL320 : Version::GL210;
+    attachShader(Shader::fromData(v, Shader::Type::Vertex, rs.get("PhongShader.vert")));
+    attachShader(Shader::fromData(v, Shader::Type::Fragment, rs.get("PhongShader.frag")));
+
+    if(!Context::current()->isExtensionSupported<Extensions::GL::ARB::explicit_attrib_location>()) {
+        bindAttributeLocation(Position::Location, "position");
+        bindAttributeLocation(Normal::Location, "normal");
+    }
 
     link();
 

src/Shaders/PhongShader.frag

@@ -1,3 +1,8 @@
+#if __VERSION__ == 120
+#define in varying
+#define color gl_FragColor
+#endif
+
 uniform vec3 ambientColor = vec3(0.0, 0.0, 0.0);
 uniform vec3 diffuseColor;
 uniform vec3 specularColor = vec3(1.0, 1.0, 1.0);
@@ -8,7 +13,9 @@ in vec3 transformedNormal;
 in vec3 lightDirection;
 in vec3 cameraDirection;
 
+#if __VERSION__ != 120
 out vec4 color;
+#endif
 
 void main() {
     /* Ambient color */

src/Shaders/PhongShader.h

@@ -30,8 +30,8 @@ namespace Magnum { namespace Shaders {
 /**
 @brief Phong shader
 
-@requires_gl33 The shader is written in GLSL 3.3, although it should be trivial
-    to port it to older versions.
+If supported, uses GLSL 3.20 and @extension{ARB,explicit_attrib_location},
+otherwise falls back to GLSL 1.20.
 */
 class SHADERS_EXPORT PhongShader: public AbstractShaderProgram {
     public:

src/Shaders/PhongShader.vert

@@ -1,9 +1,20 @@
+#if __VERSION__ == 120
+#define in attribute
+#define out varying
+#endif
+
 uniform mat4 transformationMatrix;
 uniform mat4 projectionMatrix;
 uniform vec3 light;
 
+#if __VERSION__ != 120 && defined(GL_ARB_explicit_attrib_location)
+#extension GL_ARB_explicit_attrib_location: enable
 layout(location = 0) in vec4 position;
 layout(location = 1) in vec3 normal;
+#else
+in vec4 position;
+in vec3 normal;
+#endif
 
 out vec3 transformedNormal;
 out vec3 lightDirection;