Use high precision floating point variables if possible.

On desktop medium and high precision is generally the same, at least for mesa drivers. But on some Android devices medium precision is much worse, which causes artifacts. We need high precision float variables in vertex shaders for proper scene rendering. Setting different precision for fragment and vertex shaders seems to be not possible, so we just set it to high for both shader types when it's available.

src/graphics/shader.cpp

@@ -107,11 +107,17 @@ GLuint ShaderBase::loadShader(const std::string &file, unsigned type)
     if (CVS->needsRGBBindlessWorkaround())
         code << "#define SRGBBindlessFix\n";
 
+#if !defined(USE_GLES2)
     //shader compilation fails with some drivers if there is no precision qualifier
     if (type == GL_FRAGMENT_SHADER)
         code << "precision mediump float;\n";
-#if defined(USE_GLES2)
-    else if (type == GL_VERTEX_SHADER)
+#else
+    int range[2], precision;
+    glGetShaderPrecisionFormat(GL_FRAGMENT_SHADER, GL_HIGH_FLOAT, range, &precision);
+    
+    if (precision > 0)
+        code << "precision highp float;\n";
+    else
         code << "precision mediump float;\n";
 #endif