OpenGLHelper.cpp

#include "OpenGLHelper.h"

#include <iostream>
#include <string>

#include "imgui.h"
#include "imgui_impl_opengl3.h"
#include <SDL.h>

// below because "The declaration of a static data member in its class definition is not a definition"
OpenGLHelper* OpenGLHelper::s_instance;

//////////////////////////////////////////////////////////////////////////
// Basic singleton methods
//////////////////////////////////////////////////////////////////////////

void OpenGLHelper::Initialize()
{
	for (size_t i = 0; i < _SDHR_MAX_TEXTURES; i++)
	{
		v_texture_ids.push_back(UINT_MAX);
	}
}

OpenGLHelper::~OpenGLHelper()
{
	for (auto texid : v_texture_ids)
	{
		glDeleteTextures(1, &texid);
	}
}

//////////////////////////////////////////////////////////////////////////
// Methods
//////////////////////////////////////////////////////////////////////////

// Sets the correct gl version and returns the glsl version string
void OpenGLHelper::set_gl_version()
{
	// Decide GL+GLSL versions
#if defined(IMGUI_IMPL_OPENGL_ES2)
	// GL ES 3.0 + GLSL 300 es
    // ImGui only supports 3.0, not 3.1
	glsl_version = "#version 300 es";
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, 0);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
#elif defined(__APPLE__)
	// GL 4.1 Core + GLSL 410
	glsl_version = "#version 410";
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, SDL_GL_CONTEXT_FORWARD_COMPATIBLE_FLAG); // Always required on Mac
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 4);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 1);
#else
	// GL 4.1 Core + GLSL 410
	glsl_version = "#version 410";
	if (SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, 0) != 0)
		std::cerr << "SDL Error: " << SDL_GetError() << std::endl;
	if (SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE) != 0)
		std::cerr << "SDL Error: " << SDL_GetError() << std::endl;
	if (SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 4) != 0)
		std::cerr << "SDL Error: " << SDL_GetError() << std::endl;
	if (SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 1) != 0)
		std::cerr << "SDL Error: " << SDL_GetError() << std::endl;
#endif

}


const std::string* OpenGLHelper::get_glsl_version()
{
	return &glsl_version;
}

// This method loads the texture data into the texture specified at textureID
void OpenGLHelper::load_texture(unsigned char* data, int width, int height, int nrComponents, GLuint textureID)
{
	GLenum glerr;
	GLenum format = GL_RGBA;
	if (nrComponents == 1)
		format = GL_RED;
	else if (nrComponents == 3)
		format = GL_RGBA;
	else if (nrComponents == 4)
		format = GL_RGBA;

	glBindTexture(GL_TEXTURE_2D, textureID);
	if ((glerr = glGetError()) != GL_NO_ERROR) {
		std::cerr << "OpenGL load_texture glBindTexture error: " << glerr << std::endl;
	}
	glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);
	if ((glerr = glGetError()) != GL_NO_ERROR) {
		std::cerr << "OpenGL load_texture glTexImage2D error: " << glerr << std::endl;
	}
	// NOTE: May need to generate mipmaps in case we want to allow zooming in-out
	// But then we need to change the GL_TEXTURE_MIN_FILTER to GL_XXX_MIPMAP_XXX
	//glGenerateMipmap(GL_TEXTURE_2D);

	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);	// Note: Could also use GL_LINEAR, need to test
	if ((glerr = glGetError()) != GL_NO_ERROR) {
		std::cerr << "OpenGL load_texture glTexParameteri error: " << glerr << std::endl;
	}
}

GLuint OpenGLHelper::get_texture_id_at_slot(int slot)
{
	if (slot >= v_texture_ids.size())
	{
#ifdef DEBUG
		std::cerr << "ERROR: Requesting a texture slot above _SDHR_MAX_TEXTURES!\n";
#endif
		return UINT_MAX;
	}
	GLuint texid = v_texture_ids.at(slot);
	if (texid == UINT_MAX)
	{
		glGenTextures(1, &texid);
		v_texture_ids.at(slot) = texid;
	}
	return texid;
}