I have just "finished" learning OpenGL + glut.
I would like to try my hand at not using glut to try and get a better understanding of what goes on under the hood etc. I have been having great difficulty with the following code. I am trying to learn from a post on GitHub https://github.com/gamedevtech/X11OpenGLWindow and the example towards the end works but the triangle that it is suppose to render, does not. I thought it was because glBegin()--glEnd() are no more in current version of OpenGL. I tried to rewrite it using glDrawArrays. It did not work in the first place, what stupid thing am I doing here?
#include <iostream>
#include <cstring>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/keysymdef.h>
#include <GL/gl.h>
#include <GL/glx.h>
#include <sys/time.h>
#include <unistd.h>
#define WINDOW_WIDTH 800
#define WINDOW_HEIGHT 600
#define FPS 60
#define TEST_LOCAL
extern bool Initialize(int w, int h);
extern bool Update(float deltaTime);
extern void Render();
extern void Resize(int w, int h);
extern void Shutdown();
static void drawTriangle(void);
typedef GLXContext (*glXCreateContextAttribsARBProc)(Display*, GLXFBConfig, GLXContext, Bool, const int*);
#define SKIP_TICKS (1000 / FPS)
static double GetMilliseconds() {
static timeval s_tTimeVal;
gettimeofday(&s_tTimeVal, NULL);
double time = s_tTimeVal.tv_sec * 1000.0; // sec to ms
time += s_tTimeVal.tv_usec / 1000.0; // us to ms
return time;
}
static bool isExtensionSupported(const char *extList, const char *extension) {
return strstr(extList, extension) != 0;
}
int main(int argc, char** argv) {
Display* display;
Window window;
Screen* screen;
int screenId;
XEvent ev;
// Open the display
display = XOpenDisplay(NULL);
if (display == NULL) {
std::cout << "Could not open display\n";
return 1;
}
screen = DefaultScreenOfDisplay(display);
screenId = DefaultScreen(display);
// Check GLX version
GLint majorGLX, minorGLX = 0;
glXQueryVersion(display, &majorGLX, &minorGLX);
if (majorGLX <= 1 && minorGLX < 2) {
std::cout << "GLX 1.2 or greater is required.\n";
XCloseDisplay(display);
return 1;
}
GLint glxAttribs[] = {
GLX_X_RENDERABLE , True,
GLX_DRAWABLE_TYPE , GLX_WINDOW_BIT,
GLX_RENDER_TYPE , GLX_RGBA_BIT,
GLX_X_VISUAL_TYPE , GLX_TRUE_COLOR,
GLX_RED_SIZE , 8,
GLX_GREEN_SIZE , 8,
GLX_BLUE_SIZE , 8,
GLX_ALPHA_SIZE , 8,
GLX_DEPTH_SIZE , 24,
GLX_STENCIL_SIZE , 8,
GLX_DOUBLEBUFFER , True,
None
};
int fbcount;
GLXFBConfig* fbc = glXChooseFBConfig(display, screenId, glxAttribs, &fbcount);
if (fbc == 0) {
std::cout << "Failed to retrieve framebuffer.\n";
XCloseDisplay(display);
return 1;
}
// Pick the FB config/visual with the most samples per pixel
int best_fbc = -1, worst_fbc = -1, best_num_samp = -1, worst_num_samp = 999;
for (int i = 0; i < fbcount; ++i) {
XVisualInfo *vi = glXGetVisualFromFBConfig( display, fbc );
if ( vi != 0)
{
int samp_buf, samples;
glXGetFBConfigAttrib( display, fbc, GLX_SAMPLE_BUFFERS, &samp_buf );
glXGetFBConfigAttrib( display, fbc, GLX_SAMPLES , &samples );
if ( best_fbc < 0 || (samp_buf && samples > best_num_samp) ) {
best_fbc = i;
best_num_samp = samples;
}
if ( worst_fbc < 0 || !samp_buf || samples < worst_num_samp )
worst_fbc = i;
worst_num_samp = samples;
}
XFree( vi );
}
GLXFBConfig bestFbc = fbc[ best_fbc ];
XFree( fbc ); // Make sure to free this!
XVisualInfo* visual = glXGetVisualFromFBConfig( display, bestFbc );
if (visual == 0) {
std::cout << "Could not create correct visual window.\n";
XCloseDisplay(display);
return 1;
}
if (screenId != visual->screen) {
std::cout << "screenId(" << screenId << ") does not match visual->screen(" << visual->screen << ").\n";
XCloseDisplay(display);
return 1;
}
// Open the window
XSetWindowAttributes windowAttribs;
windowAttribs.border_pixel = BlackPixel(display, screenId);
windowAttribs.background_pixel = WhitePixel(display, screenId);
windowAttribs.override_redirect = True;
windowAttribs.colormap = XCreateColormap(display, RootWindow(display, screenId), visual->visual, AllocNone);
windowAttribs.event_mask = ExposureMask;
window = XCreateWindow(display, RootWindow(display, screenId), 0, 0, WINDOW_WIDTH, WINDOW_HEIGHT, 0, visual->depth, InputOutput, visual->visual, CWBackPixel | CWColormap | CWBorderPixel | CWEventMask, &windowAttribs);
// Redirect Close
Atom atomWmDeleteWindow = XInternAtom(display, "WM_DELETE_WINDOW", False);
XSetWMProtocols(display, window, &atomWmDeleteWindow, 1);
// Create GLX OpenGL context
glXCreateContextAttribsARBProc glXCreateContextAttribsARB = 0;
glXCreateContextAttribsARB = (glXCreateContextAttribsARBProc) glXGetProcAddressARB( (const GLubyte *) "glXCreateContextAttribsARB" );
int context_attribs[] = {
GLX_CONTEXT_MAJOR_VERSION_ARB, 3,
GLX_CONTEXT_MINOR_VERSION_ARB, 2,
GLX_CONTEXT_FLAGS_ARB, GLX_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB,
None
};
GLXContext context = 0;
const char *glxExts = glXQueryExtensionsString( display, screenId );
if (!isExtensionSupported( glxExts, "GLX_ARB_create_context")) {
std::cout << "GLX_ARB_create_context not supported\n";
context = glXCreateNewContext( display, bestFbc, GLX_RGBA_TYPE, 0, True );
}
else {
context = glXCreateContextAttribsARB( display, bestFbc, 0, true, context_attribs );
}
XSync( display, False );
// Verifying that context is a direct context
if (!glXIsDirect (display, context)) {
std::cout << "Indirect GLX rendering context obtained\n";
}
else {
std::cout << "Direct GLX rendering context obtained\n";
}
glXMakeCurrent(display, window, context);
std::cout << "GL Renderer: " << glGetString(GL_RENDERER) << "\n";
std::cout << "GL Version: " << glGetString(GL_VERSION) << "\n";
std::cout << "GLSL Version: " << glGetString(GL_SHADING_LANGUAGE_VERSION) << "\n";
if (!Initialize(WINDOW_WIDTH, WINDOW_HEIGHT)) {
glXDestroyContext(display, context);
XFree(visual);
XFreeColormap(display, windowAttribs.colormap);
XDestroyWindow(display, window);
XCloseDisplay(display);
return 1;
}
// Show the window
XClearWindow(display, window);
XMapRaised(display, window);
double prevTime = GetMilliseconds();
double currentTime = GetMilliseconds();
double deltaTime = 0.0;
timeval time;
long sleepTime = 0;
gettimeofday(&time, NULL);
long nextGameTick = (time.tv_sec * 1000) + (time.tv_usec / 1000);
// Enter message loop
while (true) {
if (XPending(display) > 0) {
XNextEvent(display, &ev);
if (ev.type == Expose) {
XWindowAttributes attribs;
XGetWindowAttributes(display, window, &attribs);
Resize(attribs.width, attribs.height);
}
if (ev.type == ClientMessage) {
if (ev.xclient.data.l[0] == atomWmDeleteWindow) {
break;
}
}
else if (ev.type == DestroyNotify) {
break;
}
}
currentTime = GetMilliseconds();
deltaTime = double(currentTime - prevTime) * 0.001;
prevTime = currentTime;
if (!Update((float)deltaTime)) {
break;
}
Render();
// Present frame
glXSwapBuffers(display, window);
// Limit Framerate
gettimeofday(&time, NULL);
nextGameTick += SKIP_TICKS;
sleepTime = nextGameTick - ((time.tv_sec * 1000) + (time.tv_usec / 1000));
usleep((unsigned int)(sleepTime / 1000));
}
std::cout << "Shutting Down\n";
Shutdown();
// Cleanup GLX
glXDestroyContext(display, context);
// Cleanup X11
XFree(visual);
XFreeColormap(display, windowAttribs.colormap);
XDestroyWindow(display, window);
XCloseDisplay(display);
return 0;
}
static float vertices2AndColors2Intertwined[] =
{
0.0, 0.0, 0.0, 0.0, 1.0, 1.0,
10.0,0.0, 0.0, 1.0, 0.0, 0.0,
10.0, 10.0, 0.0, 0.0, 1.0, 0.0
};
static void drawTriangle(void)
{
glVertexPointer(3, GL_FLOAT, 6*sizeof(float), &vertices2AndColors2Intertwined[0]);
glColorPointer(3, GL_FLOAT, 6*sizeof(float), &vertices2AndColors2Intertwined[3]);
glDrawArrays(GL_TRIANGLES, 0, 3);
}
#ifdef TEST_LOCAL
bool Initialize(int w, int h) {
glClearColor(0.5f, 0.6f, 0.7f, 1.0f);
glViewport(0, 0, w, h);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_COLOR_ARRAY);
return true;
}
bool Update(float deltaTime) {
return true;
}
void Render()
{
glClear(GL_COLOR_BUFFER_BIT);
drawTriangle();
}
void Resize(int w, int h) {
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0, 100.0, 0.0, 100.0, -1.0, 1.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
void Shutdown() {
}
#endif
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