So I've been starting with OpenGL by following this tutorial and managed to get everything to draw fine, but when I resize my viewport, the vao, vbo and shader program are unbound. I need to rebind everything and resend the buffer data, I don't know if this is the expected behaviour, but it seems a bit ridiculous to me so maybe I'm missing something. I did some searching and tried couple of different ways (with/without vaos, using glVertexAttribFormat / glVertexAttribBinding ...) with no progress.
I made a logGl functions to get as much information as I could:
void logGl() {
int value, value2;
glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &value);
std::cout << "bound buffer: " << value << std::endl;
glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &value);
std::cout << "bound vao: " << value << std::endl;
glGetIntegerv(GL_CURRENT_PROGRAM, &value);
std::cout << "bound program: " << value << std::endl;
glGetIntegerv(GL_MAJOR_VERSION, &value);
glGetIntegerv(GL_MINOR_VERSION, &value2);
std::cout << "GL version: " << value << "." << value2 << std::endl;
float data[9];
glGetBufferSubData(GL_ARRAY_BUFFER, 0, 9 * sizeof(float), data);
std::cout << "Buffer Data: ";
for (size_t i=0; i<9; i++) { std::cout << data[i] << " ";};
std::cout << std::endl;
}
this is the output:
Shader Program ID: 3
bound buffer: 1
bound vao: 1
bound program: 3
GL version: 4.6
Buffer Data: -0.5 -0.5 0 0 0.5 0 0.5 -0.5 0
changing viewport *******
bound buffer: 0
bound vao: 0
bound program: 0
GL version: 4.6
Buffer Data: 1.23555e-31 4.59163e-41 28.875 0 30.0201 0 2.05719e+32 4.55772e-41 1.23552e-31
We see everything is unbound (Here I recreate shader program)
Shader Program ID: 39
Viewport size: 0 0 801 600
In main loop, just before isssuing draw call:
bound buffer: 1
bound vao: 0
bound program: 39
GL version: 4.6
Buffer Data: 3.8357e+34 4.55772e-41 3.47159e+34 4.55772e-41 4.56443e+34 4.55772e-41 1.5695e+11 3.09e-41 1.23552e-31
Error: 1282
--------------------------------
The error code 1282 did not really provide me with any clue, I did not get any compiling / linking errors from my setShaders function.
This is my main loop, I can provide the implementations of the shader function if needed, but it's pretty much tutorial textbook..
int main() {
// Init SDL, get GL context, set initial viewport init glew ...
Systems sys = initWindow(800, 600);
// Init a buffer
float vertices[] = {
-0.5f, -0.5f, 0.0f,
0.0f, 0.5f, 0.0f,
0.5f, -0.5f, 0.0f
};
unsigned int vbo, vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao); // bind first!
glGenBuffers(1, &vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3*sizeof(float), (void *) 0);
glEnableVertexAttribArray(0);
unsigned int shader = setShaders("Shaders.txt");
logGl();
bool running = true;
while (running) {
bool log = false;
SDL_Event event;
while (SDL_PollEvent(&event)) {
switch (event.type) {
case SDL_QUIT:
running = false;
case SDL_KEYDOWN:
if (event.key.keysym.sym == SDLK_ESCAPE) running = false;
case SDL_WINDOWEVENT:
switch (event.window.event) {
case SDL_WINDOWEVENT_RESIZED:
int dims[4];
std::cout << "changing viewport ******* \n";
glViewport(0, 0, event.window.data1, event.window.data2);
// glViewport(0, 0, 500, 500);
logGl();
std::cout << "We see everything is unbound" << std::endl;
// Updating viewport unbinds vao, shader program
// and seems to empty vbo data
// since I get this error code after viewport call at glDraw:
shader = setShaders("Shaders.txt");
glUseProgram(shader);
glGetIntegerv(GL_VIEWPORT, dims);
std::cout << "Viewport size: "
<< dims[0] << " "
<< dims[1] << " "
<< dims[2] << " "
<< dims[3] << std::endl;
log = true;
}
}
}
// random bg color
Uint32 rdCol = SDL_GetPerformanceCounter();
glClearColor((float) (rdCol & 0x0000FF00) / 0x0000FF00,
(float) (rdCol & 0x00FF0000) / 0x00FF0000,
(float) (rdCol & 0xFF000000) / 0xFF000000, 1);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// Why is this not needed ..???
glBindVertexArray(vao);
///////////////////////////////////////////////////////////////////////
// *** The four lines below are necessary to keep drawing on win resize
glBindBuffer(GL_ARRAY_BUFFER, vbo);
// glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
//
// glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void *) 0);
// glEnableVertexAttribArray(0);
///////////////////////////////////////////////////////////////////////
if (log) {
std::cout << "In main loop, just before isssuing draw call:" << std::endl;
logGl();
std::cout << "Error: " << glGetError() << std::endl;
std::cout << "--------------------------------" << std::endl;
}
glDrawArrays(GL_TRIANGLES, 0, 3);
/* 'flip' Window */
SDL_GL_SwapWindow(sys.window);
}
SDL_FreeSurface(sys.winSurf);
SDL_DestroyWindow(sys.window);
SDL_Quit();
return 0;
}
So the big question is why eveything gets unbound when I call glViewport, as I would believe it should keep drawing only by binding vao and vbo (which works until I resize the window)
