Chapter2.3.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <GL/glew.h>
#include <GL/freeglut.h>
#define WINDOW_TITLE_PREFIX "Chapter 2"

int CurrentWidth = 800,
	CurrentHeight = 600,
	WindowHandle = 0;

unsigned FrameCount = 0;

GLuint
	VertexShaderId,
	FragmentShaderId,
	ProgramId,
	VaoId,
	VboId,
	ColorBufferId;

const GLchar* VertexShader =
{
	"#version 400\n"\

	"layout(location=0) in vec4 in_Position;\n"\
	"layout(location=1) in vec4 in_Color;\n"\
	"out vec4 ex_Color;\n"\

	"void main(void)\n"\
	"{\n"\
	"	gl_Position = in_Position;\n"\
	"	ex_Color = in_Color;\n"\
	"}\n"
};

const GLchar* FragmentShader =
{
	"#version 400\n"\

	"in vec4 ex_Color;\n"\
	"out vec4 out_Color;\n"\

	"void main(void)\n"\
	"{\n"\
	"	out_Color = ex_Color;\n"\
	"}\n"
};

void Initialize(int, char*[]);
void InitWindow(int, char*[]);
void ResizeFunction(int, int);
void RenderFunction(void);
void TimerFunction(int);
void IdleFunction(void);
void Cleanup(void);
void CreateVBO(void);
void DestroyVBO(void);
void CreateShaders(void);
void DestroyShaders(void);

int main(int argc, char* argv[])
{
	Initialize(argc, argv);

	glutMainLoop();
	
	exit(EXIT_SUCCESS);
}

void Initialize(int argc, char* argv[])
{
	GLenum GlewInitResult;
	
	glewExperimental = GL_TRUE;
	InitWindow(argc, argv);

	GlewInitResult = glewInit();

	if (GLEW_OK != GlewInitResult) {
		fprintf(
			stderr,
			"ERROR: %s\n",
			glewGetErrorString(GlewInitResult)
		);
		exit(EXIT_FAILURE);
	}
	
	fprintf(
		stdout,
		"INFO: OpenGL Version: %s\n",
		glGetString(GL_VERSION)
	);

	CreateShaders();
	CreateVBO();

	glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
}

void InitWindow(int argc, char* argv[])
{
	glutInit(&argc, argv);
	
	glutInitContextVersion(4, 0);
	glutInitContextFlags(GLUT_FORWARD_COMPATIBLE);
	glutInitContextProfile(GLUT_CORE_PROFILE);

	glutSetOption(
		GLUT_ACTION_ON_WINDOW_CLOSE,
		GLUT_ACTION_GLUTMAINLOOP_RETURNS
	);
	
	glutInitWindowSize(CurrentWidth, CurrentHeight);

	glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);

	WindowHandle = glutCreateWindow(WINDOW_TITLE_PREFIX);

	if(WindowHandle < 1) {
		fprintf(
			stderr,
			"ERROR: Could not create a new rendering window.\n"
		);
		exit(EXIT_FAILURE);
	}
	
	glutReshapeFunc(ResizeFunction);
	glutDisplayFunc(RenderFunction);
	glutIdleFunc(IdleFunction);
	glutTimerFunc(0, TimerFunction, 0);
	glutCloseFunc(Cleanup);
}

void ResizeFunction(int Width, int Height)
{
	CurrentWidth = Width;
	CurrentHeight = Height;
	glViewport(0, 0, CurrentWidth, CurrentHeight);
}

void RenderFunction(void)
{
	++FrameCount;

	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	
	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

	glutSwapBuffers();
	glutPostRedisplay();
}

void IdleFunction(void)
{
	glutPostRedisplay();
}

void TimerFunction(int Value)
{
	if (0 != Value) {
		char* TempString = (char*)
			malloc(512 + strlen(WINDOW_TITLE_PREFIX));

		sprintf(
			TempString,
			"%s: %d Frames Per Second @ %d x %d",
			WINDOW_TITLE_PREFIX,
			FrameCount * 4,
			CurrentWidth,
			CurrentHeight
		);

		glutSetWindowTitle(TempString);
		free(TempString);
	}
	
	FrameCount = 0;
	glutTimerFunc(250, TimerFunction, 1);
}

void Cleanup(void)
{
	DestroyShaders();
	DestroyVBO();
}

void CreateVBO(void)
{
	GLfloat Vertices[] = {
		-0.8f,  0.8f, 0.0f, 1.0f,
		 0.8f,  0.8f, 0.0f, 1.0f,
		-0.8f, -0.8f, 0.0f, 1.0f,
		 0.8f, -0.8f, 0.0f, 1.0f
	};

	GLfloat Colors[] = {
		1.0f, 0.0f, 0.0f, 1.0f,
		0.0f, 1.0f, 0.0f, 1.0f,
		0.0f, 0.0f, 1.0f, 1.0f,
		1.0f, 1.0f, 1.0f, 1.0f
	};

	GLenum ErrorCheckValue = glGetError();
	
	glGenVertexArrays(1, &VaoId);
	glBindVertexArray(VaoId);

	glGenBuffers(1, &VboId);
	glBindBuffer(GL_ARRAY_BUFFER, VboId);
	glBufferData(GL_ARRAY_BUFFER, sizeof(Vertices), Vertices, GL_STATIC_DRAW);
	glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 0, 0);
	glEnableVertexAttribArray(0);
	
	glGenBuffers(1, &ColorBufferId);
	glBindBuffer(GL_ARRAY_BUFFER, ColorBufferId);
	glBufferData(GL_ARRAY_BUFFER, sizeof(Colors), Colors, GL_STATIC_DRAW);
	glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 0, 0);
	glEnableVertexAttribArray(1);

	ErrorCheckValue = glGetError();
	if (ErrorCheckValue != GL_NO_ERROR)
	{
		fprintf(
			stderr,
			"ERROR: Could not create a VBO: %s \n",
			gluErrorString(ErrorCheckValue)
		);

		exit(-1);
	}
}

void DestroyVBO(void)
{
	GLenum ErrorCheckValue = glGetError();

	glDisableVertexAttribArray(1);
	glDisableVertexAttribArray(0);
	
	glBindBuffer(GL_ARRAY_BUFFER, 0);

	glDeleteBuffers(1, &ColorBufferId);
	glDeleteBuffers(1, &VboId);

	glBindVertexArray(0);
	glDeleteVertexArrays(1, &VaoId);

	ErrorCheckValue = glGetError();
	if (ErrorCheckValue != GL_NO_ERROR)
	{
		fprintf(
			stderr,
			"ERROR: Could not destroy the VBO: %s \n",
			gluErrorString(ErrorCheckValue)
		);

		exit(-1);
	}
}

void CreateShaders(void)
{
	GLenum ErrorCheckValue = glGetError();
	
	VertexShaderId = glCreateShader(GL_VERTEX_SHADER);
	glShaderSource(VertexShaderId, 1, &VertexShader, NULL);
	glCompileShader(VertexShaderId);

	FragmentShaderId = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(FragmentShaderId, 1, &FragmentShader, NULL);
	glCompileShader(FragmentShaderId);

	ProgramId = glCreateProgram();
		glAttachShader(ProgramId, VertexShaderId);
		glAttachShader(ProgramId, FragmentShaderId);
	glLinkProgram(ProgramId);
	glUseProgram(ProgramId);

	ErrorCheckValue = glGetError();
	if (ErrorCheckValue != GL_NO_ERROR)
	{
		fprintf(
			stderr,
			"ERROR: Could not create the shaders: %s \n",
			gluErrorString(ErrorCheckValue)
		);

		exit(-1);
	}
}

void DestroyShaders(void)
{
	GLenum ErrorCheckValue = glGetError();

	glUseProgram(0);

	glDetachShader(ProgramId, VertexShaderId);
	glDetachShader(ProgramId, FragmentShaderId);

	glDeleteShader(FragmentShaderId);
	glDeleteShader(VertexShaderId);

	glDeleteProgram(ProgramId);

	ErrorCheckValue = glGetError();
	if (ErrorCheckValue != GL_NO_ERROR)
	{
		fprintf(
			stderr,
			"ERROR: Could not destroy the shaders: %s \n",
			gluErrorString(ErrorCheckValue)
		);

		exit(-1);
	}
}