// compute shaders tutorial
// Dr Anton Gerdelan <gerdela@scss.tcd.ie>
// Trinity College Dublin, Ireland
// 26 Feb 2016

#include "gl_utils.h"

GLFWwindow *window;

bool start_gl() {
	{ // glfw
		if ( !glfwInit() ) {
			fprintf( stderr, "ERROR: could not start GLFW3\n" );
			return false;
		}
		glfwWindowHint( GLFW_CONTEXT_VERSION_MAJOR, 4 );
		glfwWindowHint( GLFW_CONTEXT_VERSION_MINOR, 3 );
		glfwWindowHint( GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE );
		glfwWindowHint( GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE );
		window = glfwCreateWindow( WINDOW_W, WINDOW_H, "compute shaders tutorial", NULL,
															 NULL );
		if ( !window ) {
			fprintf( stderr, "ERROR: could not open window with GLFW3\n" );
			glfwTerminate();
			return false;
		}
		glfwMakeContextCurrent( window );
	}
	{ // glew
		glewExperimental = GL_TRUE;
		glewInit();
	}
	const GLubyte *renderer = glGetString( GL_RENDERER );
	const GLubyte *version = glGetString( GL_VERSION );
	printf( "Renderer: %s\n", renderer );
	printf( "OpenGL version %s\n", version );
	return true;
}

void stop_gl() { glfwTerminate(); }

void print_shader_info_log( GLuint shader ) {
	int max_length = 4096;
	int actual_length = 0;
	char slog[4096];
	glGetShaderInfoLog( shader, max_length, &actual_length, slog );
	fprintf( stderr, "shader info log for GL index %u\n%s\n", shader, slog );
}

void print_program_info_log( GLuint program ) {
	int max_length = 4096;
	int actual_length = 0;
	char plog[4096];
	glGetProgramInfoLog( program, max_length, &actual_length, plog );
	fprintf( stderr, "program info log for GL index %u\n%s\n", program, plog );
}

bool check_shader_errors( GLuint shader ) {
	GLint params = -1;
	glGetShaderiv( shader, GL_COMPILE_STATUS, &params );
	if ( GL_TRUE != params ) {
		fprintf( stderr, "ERROR: shader %u did not compile\n", shader );
		print_shader_info_log( shader );
		return false;
	}
	return true;
}

bool check_program_errors( GLuint program ) {
	GLint params = -1;
	glGetProgramiv( program, GL_LINK_STATUS, &params );
	if ( GL_TRUE != params ) {
		fprintf( stderr, "ERROR: program %u did not link\n", program );
		print_program_info_log( program );
		return false;
	}
	return true;
}

GLuint create_quad_vao() {
	GLuint vao = 0, vbo = 0;
	float verts[] = { -1.0f, -1.0f, 0.0f, 0.0f, -1.0f, 1.0f, 0.0f, 1.0f,
										1.0f,	-1.0f, 1.0f, 0.0f, 1.0f,	1.0f, 1.0f, 1.0f };
	glGenBuffers( 1, &vbo );
	glBindBuffer( GL_ARRAY_BUFFER, vbo );
	glBufferData( GL_ARRAY_BUFFER, 16 * sizeof( float ), verts, GL_STATIC_DRAW );
	glGenVertexArrays( 1, &vao );
	glBindVertexArray( vao );
	glEnableVertexAttribArray( 0 );
	GLintptr stride = 4 * sizeof( float );
	glVertexAttribPointer( 0, 2, GL_FLOAT, GL_FALSE, stride, NULL );
	glEnableVertexAttribArray( 1 );
	GLintptr offset = 2 * sizeof( float );
	glVertexAttribPointer( 1, 2, GL_FLOAT, GL_FALSE, stride, (GLvoid *)offset );
	return vao;
}

// this is the quad's vertex shader in an ugly C string
const char *vert_shader_str =
	"#version 430\n                                                               \
layout (location = 0) in vec2 vp;\n                                           \
layout (location = 1) in vec2 vt;\n                                           \
out vec2 st;\n                                                                \
\n                                                                            \
void main () {\n                                                              \
  st = vt;\n                                                                  \
  gl_Position = vec4 (vp, 0.0, 1.0);\n                                        \
}\n";

// this is the quad's fragment shader in an ugly C string
const char *frag_shader_str =
	"#version 430\n                                                               \
in vec2 st;\n                                                                 \
uniform sampler2D img;\n                                                      \
out vec4 fc;\n                                                                \
\n                                                                            \
void main () {\n                                                              \
  fc = texture (img, st);\n                                                 \
}\n";

GLuint create_quad_program() {
	GLuint program = glCreateProgram();
	GLuint vert_shader = glCreateShader( GL_VERTEX_SHADER );
	glShaderSource( vert_shader, 1, &vert_shader_str, NULL );
	glCompileShader( vert_shader );
	check_shader_errors( vert_shader ); // code moved to gl_utils.cpp
	glAttachShader( program, vert_shader );
	GLuint frag_shader = glCreateShader( GL_FRAGMENT_SHADER );
	glShaderSource( frag_shader, 1, &frag_shader_str, NULL );
	glCompileShader( frag_shader );
	check_shader_errors( frag_shader ); // code moved to gl_utils.cpp
	glAttachShader( program, frag_shader );
	glLinkProgram( program );
	check_program_errors( program ); // code moved to gl_utils.cpp
	return program;
}