# OpenGL Random glClearColor values

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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:

[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;
}
[/CODE]

thank you. Edited by lucaswrk

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[quote name='lucaswrk' timestamp='1344194233' post='4966437']
glClearColor(rand()%256, rand()%256, rand()%256, 1.0);
[/quote]
Your alpha value is 1.0. You probably meant 255 [img]http://public.gamedev.net//public/style_emoticons/default/smile.png[/img].

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 [tt]rand()%256[/tt] 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.) Edited by jouley

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[quote name='jouley' timestamp='1344195027' post='4966442']
[quote name='lucaswrk' timestamp='1344194233' post='4966437']
glClearColor(rand()%256, rand()%256, rand()%256, 1.0);
[/quote]
Your alpha value is 1.0. You probably meant 255 [img]http://public.gamedev.net//public/style_emoticons/default/smile.png[/img].

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 [tt]rand()%256[/tt] 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..

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

thank you @jouley!

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