Texture with unwanted colour - c

Question

I'm trying to learn how to use textures in OpenGL.I don't have freeimage installed so I had to create the bitmap with a for loop.
What I'm trying to do is to simply take a texture with all red points, and to map it inside a square:
#import <OpenGL/OpenGL.h>
#import <GLUT/GLUT.h>
#import <stdlib.h>
#import <string.h>
#import <math.h>
GLuint texture;
GLfloat (*pixels) [3];
void init()
{
// Inizializzazione
glEnable(GL_DEPTH_TEST);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45, 1, 1, 1000);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(0, 0, -100, 0, 0, 0, 0, 1, 0);
// Inizializzazione della texture
glGenTextures(1, &texture);
pixels= malloc(256*256*sizeof(GLfloat[3]));
for(GLuint i=0; i<256*256;i++)
{
pixels[i][0]=1.0;
pixels[i][1]= pixels[i][2]= 0.0;
}
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 256, 256, 0, GL_RGB, GL_FLOAT, pixels);
}
void display()
{
glClearColor(0, 0, 0, 0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, texture);
glPushMatrix();
glBegin(GL_QUADS);
glVertex3f(0, 0, 0);
glTexCoord2f(0.0, 0.0);
glVertex3f(10, 0, 0);
glTexCoord2f(0.0, 1.0);
glVertex3f(10, 10, 0);
glTexCoord2f(1.0, 1.0);
glVertex3f(0, 10, 0);
glTexCoord2f(0.0, 1.0);
glEnd();
glPopMatrix();
glDisable(GL_TEXTURE_2D);
glutSwapBuffers();
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE);
glutInitWindowPosition(100, 100);
glutInitWindowSize(600, 600);
glutCreateWindow(argv[0]);
glutDisplayFunc(display);
init();
glutMainLoop();
free(pixels);
return 0;
}
The problem is that all the pixels are red, but I get a white square instead of a red one:

Answer 1

You need to bind the texture before you upload data to it, so use glBindTexture before glTexImage2D. Also as it stands the texture will be incomplete, since it has no mipmaps and the default values for minification and magnification filters require them. Use glTexParameter to set the filters to linear, or otherwise create mipmaps.

Answer 2

Give this a shot:
#include <GL/glut.h>
GLuint texture;
void init()
{
// Inizializzazione della texture
unsigned int i;
GLfloat* pixels = (GLfloat*)malloc( 256 * 256 * sizeof( GLfloat ) * 3 );
for( i = 0; i < 256 * 256; i++ )
{
GLuint base = i * 3;
pixels[ base + 0 ] = 1.0f;
pixels[ base + 1 ] = 0.0f;
pixels[ base + 2 ] = 0.0f;
}
glGenTextures(1, &texture);
glBindTexture( GL_TEXTURE_2D, texture );
// disable mipmap filtering since we aren't uploading mipmaps
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
glTexImage2D( GL_TEXTURE_2D, 0, GL_RGB, 256, 256, 0, GL_RGB, GL_FLOAT, pixels );
free( pixels);
}
void display( void )
{
glClearColor(0, 0, 0, 0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45, 1, 1, 1000);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(0, 0, -100, 0, 0, 0, 0, 1, 0);
glEnable(GL_DEPTH_TEST);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, texture);
// important because GL_TEXTURE_ENV defaults to GL_MODULATE
glColor3ub(255,255,255);
glPushMatrix();
glBegin(GL_QUADS);
glVertex3f(0, 0, 0);
glTexCoord2f(0.0, 0.0);
glVertex3f(10, 0, 0);
glTexCoord2f(0.0, 1.0);
glVertex3f(10, 10, 0);
glTexCoord2f(1.0, 1.0);
glVertex3f(0, 10, 0);
glTexCoord2f(0.0, 1.0);
glEnd();
glPopMatrix();
glDisable(GL_TEXTURE_2D);
glutSwapBuffers();
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE);
glutInitWindowPosition(100, 100);
glutInitWindowSize(600, 600);
glutCreateWindow(argv[0]);
init();
glutDisplayFunc(display);
glutMainLoop();
return 0;
}