Enabled only one instance of each shader type per shader program. Closes #37

src/libraries/core/base/program.cpp

@@ -5,7 +5,12 @@ namespace glare::core
 	Program::Program(const std::vector<std::shared_ptr<Shader>> &shaders)
 	{
 		for (const auto &shader : shaders)
+		{
+			if (m_shader_stages.find(shader->type()) != m_shader_stages.end())
+				throw std::invalid_argument("Can't attach more than one of shader type id " + std::to_string(static_cast<unsigned>(shader->type())) + " to a program.");
 			gl::attachShader(m_handle, shader->id());
+			m_shader_stages.insert(shader->type());
+		}
 
 		gl::linkProgram(m_handle);
 		int success = 0;
@@ -80,7 +85,6 @@ namespace glare::core
 	{
 		for (auto &&shader : shaders)
 		{
-			m_shader_stages.push_back(shader->type());
 			int num_subroutines;
 			gl::getProgramStageiv(m_handle, shader->type(), gl::ProgramParameter::eActiveSubroutines, &num_subroutines);
 			int max_length;

src/libraries/core/base/program.h

@@ -3,6 +3,7 @@
 
 #include <map>
 #include <string>
+#include <set>
 
 #include <glm/ext.hpp>
 #include <util/opengl.h>
@@ -93,7 +94,7 @@ namespace glare::core
 		gl::handle::shader_program m_handle;
 		std::map<std::string, UniformInfo> m_uniforms;
 		std::map<std::string, std::map<gl::ShaderType, SubroutineInfo>> m_subroutines;
-		std::vector<gl::ShaderType> m_shader_stages;
+		std::set<gl::ShaderType> m_shader_stages;
 		std::map<gl::ShaderType, std::vector<unsigned>> m_subroutine_bindings;
 	};