🔒 Locked

Random glClearColor values

Started by lucaswrk Aug 5, 2012 at 7:17 PM 1 replies 4k views

Original Post

Aug 5, 2012 at 7:17 PM

hello everyone, i'm new to opengl and im having trouble to generate glClearColor random values... if i set it manually, works well but with rand()%256 it not. Whats going on ?

os: ubuntu 12.04
io/window library: sdl

heres my code:


 #include <iostream>
 #include "SDL/SDL.h"
 #include "SDL/SDL_opengl.h"
 #include <stdlib.h>
 #include <time.h>
 using namespace std;
 int main()
 {
 srand(time(NULL));
 SDL_Init(SDL_INIT_EVERYTHING);
 SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8);
 SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 8);
 SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);
 SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
 SDL_GL_SetAttribute(SDL_GL_BUFFER_SIZE, 32);
 SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 16);
 SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
 SDL_WM_SetCaption("Our first game", NULL);
 SDL_SetVideoMode(600, 400, 32, SDL_OPENGL);
 glClearColor(255,255,255,255); //rgba
 glViewport(0, 0, 600, 400); // top-left bottom-right viewport range
 glShadeModel(GL_SMOOTH); // gradient
 
 glMatrixMode(GL_PROJECTION); // 2d
 glLoadIdentity();
 glDisable(GL_DEPTH_TEST);
 bool isRunning = true;
 SDL_Event event;
 while(isRunning)
 {
 while(SDL_PollEvent(&event))
 {
 switch(event.type)
 {
 case SDL_QUIT:
 isRunning = false;
 break; 
 }
 if(event.type == SDL_KEYUP && event.key.keysym.sym == SDLK_ESCAPE)
 {
 isRunning = false;
 break;
 }
 if(event.type == SDL_KEYUP && event.key.keysym.sym == SDLK_r)
 {
 glClearColor(rand()%256, rand()%256, rand()%256, 1.0);
 break;
 }
 }
 //rendering
 glClear(GL_COLOR_BUFFER_BIT);
 SDL_GL_SwapBuffers();
 }
 SDL_Quit();
 return 0;
 }

thank you.

jouley

Aug 5, 2012 at 7:30 PM

glClearColor(rand()%256, rand()%256, rand()%256, 1.0);

Your alpha value is 1.0. You probably meant 255

lucaswrk

Aug 5, 2012 at 7:57 PM

[quote name='lucaswrk' timestamp='1344194233' post='4966437']
glClearColor(rand()%256, rand()%256, rand()%256, 1.0);

Your alpha value is 1.0. You probably meant 255

.

Edit: It's also possible that glClearColor expects floats clamped to 1.0, in which case it's highly likely you're always getting white since rand()%256 will usually be nonzero. Try dividing the results of that calculation by 255.0f to find out. (Or check the documentation... either way, don't mix clamped floats and integer formats.)
[/quote]

yeah, that was the problem! x >= 1.0 will be the color max value, that's why my screen was getting white every time. Exactly as you said.
heres the correct code (with jouley's hint), if someone is interested..


 float r = rand()%256 / 255.0f;
 float g = rand()%256 / 255.0f;
 float b = rand()%256 / 255.0f;
 glClearColor(r, g, b, 1.0);

thank you @jouley!

Topic Locked

This topic has been locked by a moderator. New replies are not allowed.