shaders/main.cpp

#include <iostream>

#include <string>
#include <fstream>
#include <streambuf>

#include <SDL2/SDL.h>
#include <SDL2/SDL_image.h>

#ifdef __APPLE__
#include "CoreFoundation/CoreFoundation.h"
#include <OpenGL/OpenGL.h>

#if ESSENTIAL_GL_PRACTICES_SUPPORT_GL3
#include <OpenGL/gl3.h>
#else
#include <OpenGL/gl.h>
#endif //!ESSENTIAL_GL_PRACTICES_SUPPORT_GL3
#else
#include <SDL2/SDL_opengl.h>
#include <SDL2/SDL_opengl_glext.h>
#endif

const int WIN_WIDTH = 640;
const int WIN_HEIGHT = 480;

const int WORLD_WIDTH = 320;
const int WORLD_HEIGHT = 240;

struct sprite {
	float x;
	float y;
	float vx;
	float vy;
};

const int MAX_SPRITES = 20;

#ifndef __APPLE__

// I'm avoiding the use of GLEW or some extensions handler, but that 
// doesn't mean you should...
PFNGLCREATESHADERPROC glCreateShader;
PFNGLSHADERSOURCEPROC glShaderSource;
PFNGLCOMPILESHADERPROC glCompileShader;
PFNGLGETSHADERIVPROC glGetShaderiv;
PFNGLGETSHADERINFOLOGPROC glGetShaderInfoLog;
PFNGLDELETESHADERPROC glDeleteShader;
PFNGLATTACHSHADERPROC glAttachShader;
PFNGLCREATEPROGRAMPROC glCreateProgram;
PFNGLLINKPROGRAMPROC glLinkProgram;
PFNGLVALIDATEPROGRAMPROC glValidateProgram;
PFNGLGETPROGRAMIVPROC glGetProgramiv;
PFNGLGETPROGRAMINFOLOGPROC glGetProgramInfoLog;
PFNGLUSEPROGRAMPROC glUseProgram;

bool initGLExtensions() {
	glCreateShader = (PFNGLCREATESHADERPROC)SDL_GL_GetProcAddress("glCreateShader");
	glShaderSource = (PFNGLSHADERSOURCEPROC)SDL_GL_GetProcAddress("glShaderSource");
	glCompileShader = (PFNGLCOMPILESHADERPROC)SDL_GL_GetProcAddress("glCompileShader");
	glGetShaderiv = (PFNGLGETSHADERIVPROC)SDL_GL_GetProcAddress("glGetShaderiv");
	glGetShaderInfoLog = (PFNGLGETSHADERINFOLOGPROC)SDL_GL_GetProcAddress("glGetShaderInfoLog");
	glDeleteShader = (PFNGLDELETESHADERPROC)SDL_GL_GetProcAddress("glDeleteShader");
	glAttachShader = (PFNGLATTACHSHADERPROC)SDL_GL_GetProcAddress("glAttachShader");
	glCreateProgram = (PFNGLCREATEPROGRAMPROC)SDL_GL_GetProcAddress("glCreateProgram");
	glLinkProgram = (PFNGLLINKPROGRAMPROC)SDL_GL_GetProcAddress("glLinkProgram");
	glValidateProgram = (PFNGLVALIDATEPROGRAMPROC)SDL_GL_GetProcAddress("glValidateProgram");
	glGetProgramiv = (PFNGLGETPROGRAMIVPROC)SDL_GL_GetProcAddress("glGetProgramiv");
	glGetProgramInfoLog = (PFNGLGETPROGRAMINFOLOGPROC)SDL_GL_GetProcAddress("glGetProgramInfoLog");
	glUseProgram = (PFNGLUSEPROGRAMPROC)SDL_GL_GetProcAddress("glUseProgram");

	return glCreateShader && glShaderSource && glCompileShader && glGetShaderiv && 
		glGetShaderInfoLog && glDeleteShader && glAttachShader && glCreateProgram &&
		glLinkProgram && glValidateProgram && glGetProgramiv && glGetProgramInfoLog &&
		glUseProgram;
}

#endif

GLuint compileShader(const char* source, GLuint shaderType) {
	//std::cout << "Compilando shader:" << std::endl << source << std::endl;
	// Create ID for shader
	GLuint result = glCreateShader(shaderType);
	// Define shader text
	glShaderSource(result, 1, &source, NULL);
	// Compile shader
	glCompileShader(result);

	//Check vertex shader for errors
	GLint shaderCompiled = GL_FALSE;
	glGetShaderiv( result, GL_COMPILE_STATUS, &shaderCompiled );
	if( shaderCompiled != GL_TRUE ) {
		std::cout << "Error en la compilación: " << result << "!" << std::endl;
		GLint logLength;
		glGetShaderiv(result, GL_INFO_LOG_LENGTH, &logLength);
		if (logLength > 0)
		{
			GLchar *log = (GLchar*)malloc(logLength);
			glGetShaderInfoLog(result, logLength, &logLength, log);
			std::cout << "Shader compile log:" << log << std::endl;
			free(log);
		}
		glDeleteShader(result);
		result = 0;
	} else {
		std::cout << "Shader compilado correctamente. Id = " << result << std::endl;
	}
	return result;
}

GLuint compileProgram(const char* vtxFile, const char* fragFile) {
	GLuint programId = 0;
	GLuint vtxShaderId, fragShaderId;

	programId = glCreateProgram();

	std::ifstream f(vtxFile);
	std::string source((std::istreambuf_iterator<char>(f)),
						std::istreambuf_iterator<char>());
	vtxShaderId = compileShader(source.c_str(), GL_VERTEX_SHADER);
	
	f=std::ifstream(fragFile);
	source=std::string((std::istreambuf_iterator<char>(f)), 
						std::istreambuf_iterator<char>());
	fragShaderId = compileShader(source.c_str(), GL_FRAGMENT_SHADER);

	if(vtxShaderId && fragShaderId) {
		// Associate shader with program
		glAttachShader(programId, vtxShaderId);
		glAttachShader(programId, fragShaderId);
		glLinkProgram(programId);
		glValidateProgram(programId);

		// Check the status of the compile/link
		GLint logLen;
		glGetProgramiv(programId, GL_INFO_LOG_LENGTH, &logLen);
		if(logLen > 0) {
			char* log = (char*) malloc(logLen * sizeof(char));
			// Show any errors as appropriate
			glGetProgramInfoLog(programId, logLen, &logLen, log);
			std::cout << "Prog Info Log: " << std::endl << log << std::endl;
			free(log);
		}
	}
	if(vtxShaderId) {
		glDeleteShader(vtxShaderId);
	}
	if(fragShaderId) {
		glDeleteShader(fragShaderId);
	}
	return programId;
}

void presentBackBuffer(SDL_Renderer *renderer, SDL_Window* win, SDL_Texture* backBuffer, GLuint programId) {
	GLint oldProgramId;
	// Guarrada para obtener el textureid (en driverdata->texture)
	//Detach the texture
	SDL_SetRenderTarget(renderer, NULL);
	SDL_RenderClear(renderer);

	SDL_GL_BindTexture(backBuffer, NULL, NULL);
	if(programId != 0) {
		glGetIntegerv(GL_CURRENT_PROGRAM,&oldProgramId);
		glUseProgram(programId);
	}

	GLfloat minx, miny, maxx, maxy;
	GLfloat minu, maxu, minv, maxv;

	// Coordenadas de la ventana donde pintar.
	minx = 0.0f;
	miny = 0.0f;
	maxx = WORLD_WIDTH;
	maxy = WORLD_HEIGHT;

	minu = 0.0f;
	maxu = 1.0f;
	minv = 0.0f;
	maxv = 1.0f;

    glViewport(0, 0, WIN_WIDTH, WIN_HEIGHT);

	glBegin(GL_TRIANGLE_STRIP);
		glTexCoord2f(minu, minv);
		glVertex2f(minx, miny);
		glTexCoord2f(maxu, minv);
		glVertex2f(maxx, miny);
		glTexCoord2f(minu, maxv);
		glVertex2f(minx, maxy);
		glTexCoord2f(maxu, maxv);
		glVertex2f(maxx, maxy);
	glEnd();
	SDL_GL_SwapWindow(win);

	if(programId != 0) {
		glUseProgram(oldProgramId);
	}
}

#ifdef __APPLE__
void initializeFileSystem() {
	CFBundleRef mainBundle = CFBundleGetMainBundle();
	CFURLRef resourcesURL = CFBundleCopyResourcesDirectoryURL(mainBundle);
	char path[PATH_MAX];
	if (!CFURLGetFileSystemRepresentation(resourcesURL, TRUE, (UInt8 *)path, PATH_MAX))
	{
		std::cerr << "Couldn't get file system representation! " << std::endl;
	}
	CFRelease(resourcesURL);
	chdir(path);
}
#endif

int main(int argc, char **argv){
	GLuint programId;

#ifdef __APPLE__
	initializeFileSystem();
#endif

	if (SDL_Init(SDL_INIT_EVERYTHING | SDL_VIDEO_OPENGL) != 0){
		std::cerr << "SDL_Init failed: " << SDL_GetError() << "\n";
		return 1;
	}

	SDL_Window *win = SDL_CreateWindow("Custom shader with SDL2 renderer!", SDL_WINDOWPOS_CENTERED,
		SDL_WINDOWPOS_CENTERED, WIN_WIDTH, WIN_HEIGHT, 0);

	SDL_SetHint(SDL_HINT_RENDER_DRIVER, "opengl");

	SDL_Renderer *renderer = SDL_CreateRenderer(win, -1,
		SDL_RENDERER_ACCELERATED | SDL_RENDERER_TARGETTEXTURE);

	SDL_RendererInfo rendererInfo;
	SDL_GetRendererInfo(renderer, &rendererInfo);

	if(!strncmp(rendererInfo.name, "opengl", 6)) {
		std::cout << "Es OpenGL!" << std::endl;
#ifndef __APPLE__
		// If you want to use GLEW or some other GL extension handler, do it here!
		if (!initGLExtensions()) {
			std::cout << "Couldn't init GL extensions!" << std::endl;
			SDL_Quit();
			exit(-1);
		}
#endif
		// Compilar el shader y dejarlo listo para usar.
		programId = compileProgram("std.vertex", "crt.fragment");
		std::cout << "programId = " << programId << std::endl;
	}

	//Put your own bmp image here
	SDL_Surface *bmpSurf = IMG_Load("image.png");
	SDL_Texture *bmpTex = SDL_CreateTextureFromSurface(renderer, bmpSurf);
	SDL_FreeSurface(bmpSurf);

	//Make a target texture to render too
	SDL_Texture *texTarget = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBA8888,
		SDL_TEXTUREACCESS_TARGET, WORLD_WIDTH, WORLD_HEIGHT);

	int done = 0; 
	int useShader = 0;
	SDL_Rect targetRect;

	targetRect.x = 0; targetRect.y=0; targetRect.w=32; targetRect.h=32;

	struct sprite sprites[MAX_SPRITES];

	for(int i=0;i < MAX_SPRITES;++i) {
		sprites[i].x = (float) (rand() % (WORLD_WIDTH - targetRect.w));
		sprites[i].y = (float) (rand() % (WORLD_HEIGHT - targetRect.h));
		sprites[i].vx = (float) (rand() % 5 / 10.0f) - 0.2f;
		sprites[i].vy = (float) (rand() % 5 / 10.0f) - 0.2f;
	}

	// Voy a poner el fondo blanco para que se vea el shader
	SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);

	while ( ! done ) {
		//Render to the texture
		SDL_SetRenderTarget(renderer, texTarget);
		SDL_RenderClear(renderer);

		// Pintamos MAX_SPRITES UWOLes
		struct sprite* spr;
		for(int i=0;i < MAX_SPRITES;++i) {
			spr = &(sprites[i]);
			spr->x += spr->vx;
			if(spr->x < 0) {
				spr->x = 0;
				spr->vx *= -1;
			}
			if(spr->x > WORLD_WIDTH - targetRect.w) {
				spr->x = (float) (WORLD_WIDTH - targetRect.w);
				spr->vx *= -1;
			}
			spr->y += spr->vy;
			if(spr->y < 0) {
				spr->y = 0;
				spr->vy *= -1;
			}
			if(spr->y > WORLD_HEIGHT - targetRect.h) {
				spr->y = (float) (WORLD_HEIGHT - targetRect.h);
				spr->vy *= -1;
			}
			
			targetRect.x = (int)spr->x;
			targetRect.y = (int)spr->y;

			SDL_RenderCopy(renderer, bmpTex, NULL, &targetRect);
		}

		presentBackBuffer(renderer, win, texTarget, programId);

		/* This could go in a separate function */
		SDL_Event event;
		while ( SDL_PollEvent(&event) ) {
			if ( event.type == SDL_QUIT ) {
				done = 1;
			}
			if ( event.type == SDL_KEYDOWN ) {
				if ( event.key.keysym.sym == SDLK_SPACE ) {
					useShader ^= 1;
					std::cout << "useShader = " << (useShader ? "true" : "false") << std::endl;
				}
				if ( event.key.keysym.sym == SDLK_ESCAPE ) {
					done = 1;
				}
			}
		}
	}

	SDL_DestroyTexture(texTarget);
	SDL_DestroyTexture(bmpTex);
	SDL_DestroyRenderer(renderer);
	SDL_DestroyWindow(win);
	SDL_Quit();
	return 0;
}