DashGL

To keep the game simple, we will make the game a one hit gameover. When the player gets hit, we will draw a gameover sprite on top of the current scene. Then, we will set a boolean value to prevent the screen from being updated. If the player hit's the 'R' key during this state, we will reset all of the positions to default and allow the game loop to pass.

#include <stdlib.h>
#include <epoxy/gl.h>
#include <epoxy/glx.h>
#include <gtk/gtk.h>
#include <math.h>
#include "DashGL/dashgl.h"

static void on_realize(GtkGLArea *area);
static void on_render(GtkGLArea *area, GdkGLContext *context);
static gboolean on_idle(gpointer data);
static gboolean on_keydown(GtkWidget *widget, GdkEventKey *event);
static gboolean on_keyup(GtkWidget *widget, GdkEventKey *event);
static void detect_player_hit(vec3 point);
static void reset_game();

#define WIDTH 640.0f
#define HEIGHT 480.0f

GLuint program;
GLuint vao;
GLint attribute_texcoord, attribute_coord2d;
GLint uniform_mytexture, uniform_mvp;

struct {
	GLuint vbo;
	GLuint tex;
	mat4 mvp;
} background;

struct {
	GLuint vbo;
	GLuint tex;
	vec3 pos;
	mat4 mvp;
	gboolean left;
	gboolean right;
	int num_bullets;
	vec3 *bullets;
	gboolean *active;
	gboolean space;
} player;

struct {
	GLuint vbo;
	GLuint tex;
	mat4 mvp;
	GLfloat dy;
} bullet;

struct {
	GLuint vbo;
	GLuint tex;
	mat4 mvp;
	vec3 *pos;
	int num_enemies;
	float dx, dy;
	gboolean *active;
} enemy;

struct {
	int num_bullets;
	gboolean *active;
	vec3 *pos;
	float dy;
	GLuint vbo;
	GLuint tex;
	mat4 mvp;
} bullets;

struct {
	GLuint vbo;
	GLuint tex;
	mat4 mvp;
	gboolean off;
} gameover;

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

	GtkWidget *window;
	GtkWidget *glArea;

	gtk_init(&argc, &argv);

	// Initialize Window

	window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
	gtk_window_set_title(GTK_WINDOW(window), "Invaders Tutorial");
	gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
	gtk_window_set_default_size(GTK_WINDOW(window), 640, 480);
	gtk_window_set_type_hint(GTK_WINDOW(window), GDK_WINDOW_TYPE_HINT_UTILITY);
	g_signal_connect(window, "destroy", G_CALLBACK(gtk_main_quit), NULL);
	g_signal_connect(window, "key-press-event", G_CALLBACK(on_keydown), NULL);
	g_signal_connect(window, "key-release-event", G_CALLBACK(on_keyup), NULL);

	// Initialize GTK GL Area

	glArea = gtk_gl_area_new();
	gtk_widget_set_vexpand(glArea, TRUE);
	gtk_widget_set_hexpand(glArea, TRUE);
	g_signal_connect(glArea, "realize", G_CALLBACK(on_realize), NULL);
	g_signal_connect(glArea, "render", G_CALLBACK(on_render), NULL);
	gtk_container_add(GTK_CONTAINER(window), glArea);

	// Show widgets

	gtk_widget_show_all(window);
	gtk_main();

	return 0;

}

static void on_realize(GtkGLArea *area) {

	// Debug Message

	g_print("on realize     0\n");

	gtk_gl_area_make_current(area);
	if(gtk_gl_area_get_error(area) != NULL) {
		fprintf(stderr, "Unknown error\n");
		return;
	}

	const GLubyte *renderer = glGetString(GL_RENDER);
	const GLubyte *version = glGetString(GL_VERSION);

	g_print("Renderer: %s\n", renderer);
	g_print("OpenGL version supported %s\n", version);

	glClearColor(1.0f, 1.0f, 1.0f, 1.0f);

	glGenVertexArrays(1, &vao);
	glBindVertexArray(vao);

	// Background Sprite

	GLfloat background_vertices[] = {
		0.0, 0.0, 0.0, 0.0, 
		0.0, HEIGHT, 0.0, 1.0,
		WIDTH, HEIGHT, 1.0, 1.0,
		
		0.0, 0.0, 0.0, 0.0,
		WIDTH, HEIGHT, 1.0, 1.0,
		WIDTH, 0.0, 1.0, 0.0
	};
	
	glGenBuffers(1, &background.vbo);
	glBindBuffer(GL_ARRAY_BUFFER, background.vbo);
	glBufferData(
		GL_ARRAY_BUFFER,
		sizeof(background_vertices),
		background_vertices,
		GL_STATIC_DRAW
	);
	
	mat4_identity(background.mvp);
	background.tex = shader_load_texture("sprites/background.png");
	
	// Player Sprite

	GLfloat player_vertices[] = {
		-22.0, -22.0, 0.0, 0.0, 
		-22.0,  22.0, 0.0, 1.0,
		 22.0,  22.0, 1.0, 1.0,
		
		-22.0, -22.0, 0.0, 0.0,
		 22.0,  22.0, 1.0, 1.0,
		 22.0, -22.0, 1.0, 0.0
	};
	
	glGenBuffers(1, &player.vbo);
	glBindBuffer(GL_ARRAY_BUFFER, player.vbo);
	glBufferData(
		GL_ARRAY_BUFFER,
		sizeof(player_vertices),
		player_vertices,
		GL_STATIC_DRAW
	);
	
	player.pos[0] = WIDTH / 2;
	player.pos[1] = 30.0f;
	player.pos[2] = 0.0;
	player.left = FALSE;
	player.right = FALSE;
	
	mat4_translate(player.pos, player.mvp);
	player.tex = shader_load_texture("sprites/player.png");
	
	player.space = FALSE;
	player.num_bullets = 3;
	player.bullets = malloc(player.num_bullets * sizeof(vec3));
	player.active = malloc(player.num_bullets * sizeof(gboolean));

	int i;
	for(i = 0; i GLfloat gameover_vertices[] = {
		0.0, 0.0, 0.0, 0.0, 
		0.0, HEIGHT, 0.0, 1.0,
		WIDTH, HEIGHT, 1.0, 1.0,
		
		0.0, 0.0, 0.0, 0.0,
		WIDTH, HEIGHT, 1.0, 1.0,
		WIDTH, 0.0, 1.0, 0.0
	};
	
	glGenBuffers(1, &gameover.vbo);
	glBindBuffer(GL_ARRAY_BUFFER, gameover.vbo);
	glBufferData(
		GL_ARRAY_BUFFER,
		sizeof(gameover_vertices),
		gameover_vertices,
		GL_STATIC_DRAW
	);
	
	mat4_identity(gameover.mvp);
	gameover.tex = shader_load_texture("sprites/gameover.png");
	gameover.off = TRUE;

	// Compile Shader Program

	GLint compile_ok = GL_FALSE;
	GLint link_ok = GL_FALSE;

	const char *vs = "shader/vertex.glsl";
	const char *fs = "shader/fragment.glsl";
	program = shader_load_program(vs, fs);

	const char *attribute_name = "coord2d";
	attribute_coord2d = glGetAttribLocation(program, attribute_name);
	if(attribute_coord2d == -1) {
		fprintf(stderr, "Could not bind attribute %s\n", attribute_name);
		return;
	}

	attribute_name = "uv_coord";
	attribute_texcoord = glGetAttribLocation(program, attribute_name);
	if(attribute_texcoord == -1) {
		fprintf(stderr, "Could not bind attribute %s\n", attribute_name);
		return;
	}

	const char *uniform_name = "orthograph";
	GLint uniform_ortho = glGetUniformLocation(program, uniform_name);
	if(uniform_ortho == -1) {
		fprintf(stderr, "Could not bind uniform %s\n", uniform_name);
		return;
	}

	uniform_name = "mvp";
	uniform_mvp = glGetUniformLocation(program, uniform_name);
	if(uniform_mvp == -1) {
		fprintf(stderr, "Could not bind uniform %s\n", uniform_name);
		return;
	}

	uniform_name = "mytexture";
	uniform_mytexture = glGetUniformLocation(program, uniform_name);
	if(uniform_mytexture == -1) {
		fprintf(stderr, "Could not bind uniform %s\n", uniform_name);
		return;
	}

	glUseProgram(program);

	mat4 orthograph;
	mat4_orthagonal(WIDTH, HEIGHT, orthograph);
	glUniformMatrix4fv(uniform_ortho, 1, GL_FALSE, orthograph);

	g_timeout_add(20, on_idle, (void*)area);

}

static void on_render(GtkGLArea *area, GdkGLContext *context) {

	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	glUseProgram(program);
	glBindVertexArray(vao);

	glActiveTexture(GL_TEXTURE0);
	glBindTexture(GL_TEXTURE_2D, background.tex);
	glUniform1i(uniform_mytexture, 0);

	glUniformMatrix4fv(uniform_mvp, 1, GL_FALSE, background.mvp);

	glEnableVertexAttribArray(attribute_coord2d);
	glEnableVertexAttribArray(attribute_texcoord);

	glBindBuffer(GL_ARRAY_BUFFER, background.vbo);
	glVertexAttribPointer(
		attribute_coord2d,
		2,
		GL_FLOAT,
		GL_FALSE,
		sizeof(float) * 4,
		0
	);

	glVertexAttribPointer(
		attribute_texcoord,
		2,
		GL_FLOAT,
		GL_FALSE,
		sizeof(float) * 4,
		(void*)(sizeof(float) * 2)
	);
	glDrawArrays(GL_TRIANGLES, 0, 6);

	glActiveTexture(GL_TEXTURE0);
	glBindTexture(GL_TEXTURE_2D, player.tex);
	glUniform1i(uniform_mytexture, 0);

	mat4_translate(player.pos, player.mvp);
	glUniformMatrix4fv(uniform_mvp, 1, GL_FALSE, player.mvp);

	glBindBuffer(GL_ARRAY_BUFFER, player.vbo);
	glVertexAttribPointer(
		attribute_coord2d,
		2,
		GL_FLOAT,
		GL_FALSE,
		sizeof(float) * 4,
		0
	);

	glVertexAttribPointer(
		attribute_texcoord,
		2,
		GL_FLOAT,
		GL_FALSE,
		sizeof(float) * 4,
		(void*)(sizeof(float) * 2)
	);
	glDrawArrays(GL_TRIANGLES, 0, 6);

	glActiveTexture(GL_TEXTURE0);
	glBindTexture(GL_TEXTURE_2D, bullet.tex);
	glUniform1i(uniform_mytexture, 0);

	int i;
	for(i = 0; i if(!gameover.off) {
		return TRUE;
	}

	if(player.right) {
		player.pos[0] += 6.0f;
	}

	if(player.left) {
		player.pos[0] -= 6.0f;
	}

	if(player.pos[0] <0) {
		player.pos[0] = 0.0f;
	} else if(player.pos[0] > WIDTH) {
		player.pos[0] = WIDTH;
	}

	int i, k;
	for(i = 0; i  WIDTH || enemy.pos[i][0] <0) {
			do_switch = TRUE;
		}
		
		if(rand() % 5000 <4950) {
			continue;
		}
		
		for(k = 0; k  32.0f) {
				continue;
			}
			
			enemy.dx *= 1.05;

			player.active[i] = FALSE;
			enemy.active[k] = FALSE;

			break;
		}

	}

	for(i = 0; i keyval) {
		case GDK_KEY_Left:
			player.left = TRUE;
		break;
		case GDK_KEY_Right:
			player.right = TRUE;
		break;
		case GDK_KEY_space:
			
			if(!player.space) {
				int i;
				for(i = 0; i case GDK_KEY_r:
			if(!gameover.off) {
				reset_game();
			}
		break;
	}

}

static gboolean on_keyup(GtkWidget *widget, GdkEventKey *event) {

	switch(event->keyval) {
		case GDK_KEY_Left:
			player.left = FALSE;
		break;
		case GDK_KEY_Right:
			player.right = FALSE;
		break;
		case GDK_KEY_space:
			player.space = FALSE;
		break;
	}

}

static void detect_player_hit(vec3 point) {

	float x_dif, y_dif;

	x_dif = player.pos[0] - point[0];
	y_dif = player.pos[1] - point[1];
			
	if(hypotf(x_dif, y_dif) > 10.0f) {
		return;
	}

	gameover.off = FALSE;

}

static void reset_game() {

	
	// Player Sprite

	player.pos[0] = WIDTH / 2;
	player.pos[1] = 30.0f;
	player.pos[2] = 0.0;
	player.left = FALSE;
	player.right = FALSE;
	player.space = FALSE;

	int i;
	for(i = 0; i 

Compile with:

$ gcc -c -o DashGL/dashgl.o DashGL/dashgl.c -lepoxy -lpng -lm
$ gcc `pkg-config --cflags gtk+-3.0` main.c DashGL/dashgl.o `pkg-config --libs gtk+-3.0` \
-lepoxy -lm -lpng

Run with:

$ ./a.out