Fix gpu_shader4 for some drivers

- Add gl_InstanceID (GL_ARB_draw_instanced) support for drivers that don't implement GL_EXT_gpu_shader4 extension (e.g. mesa driver 'i915' on Pentium G3258).
- Don't emit the glsl extension GL_EXT_gpu_shader4 if it isn't supported by the driver (e.g. mesa driver 'i915'). In case the shader uses gl_VertexID, bump up the shader version to 130.

src/renderer_gl.cpp

@@ -5539,7 +5539,22 @@ BX_TRACE("%d, %d, %d, %s", _array, _srgb, _mipAutogen, getName(_format) );
 						&& s_extension[Extension::ARB_shader_texture_lod].m_supported
 						&& !bx::findIdentifierMatch(code, s_ARB_shader_texture_lod).isEmpty()
 						;
-					const bool usesGpuShader4   = !bx::findIdentifierMatch(code, s_EXT_gpu_shader4).isEmpty();
+
+					const bool usesVertexID = true
+						&& !s_extension[Extension::EXT_gpu_shader4].m_supported
+						&& !bx::findIdentifierMatch(code, "gl_VertexID").isEmpty()
+						;
+
+					const bool usesInstanceID = true
+						&& !s_extension[Extension::EXT_gpu_shader4].m_supported
+						&& !bx::findIdentifierMatch(code, "gl_InstanceID").isEmpty()
+						;
+
+					const bool usesGpuShader4 = true
+						&& s_extension[Extension::EXT_gpu_shader4].m_supported
+						&& !bx::findIdentifierMatch(code, s_EXT_gpu_shader4).isEmpty()
+						;
+
 					const bool usesGpuShader5   = !bx::findIdentifierMatch(code, s_ARB_gpu_shader5).isEmpty();
 					const bool usesIUsamplers   = !bx::findIdentifierMatch(code, s_uisamplers).isEmpty();
 					const bool usesUint         = !bx::findIdentifierMatch(code, s_uint).isEmpty();
@@ -5554,6 +5569,7 @@ BX_TRACE("%d, %d, %d, %s", _array, _srgb, _mipAutogen, getName(_format) );
 						:  usesTextureArray
 						|| usesTexture3D
 						|| usesIUsamplers
+						|| usesVertexID
 						|| usesUint
 						|| usesTexelFetch
 						|| usesGpuShader5
@@ -5580,6 +5596,11 @@ BX_TRACE("%d, %d, %d, %s", _array, _srgb, _mipAutogen, getName(_format) );
 						}
 					}
 
+					if (usesInstanceID)
+					{
+						bx::write(&writer, "#extension GL_ARB_draw_instanced : enable\n");
+					}
+
 					if (usesGpuShader4)
 					{
 						bx::write(&writer, "#extension GL_EXT_gpu_shader4 : enable\n");