Set background image of an openGL window
I'd avoid doing anything other than a glFrustum()
or glOrtho()
call for your projection matrix.
Also, set GL_UNPACK_ALIGNMENT
to 1 for your texture loading if you're doing 3-component pixels:
#include <GL/glut.h>
int w1 = 0;
int h1 = 0;
void reshape(int w, int h)
{
w1 = w;
h1 = h;
glViewport(0, 0, w, h);
}
void orthogonalStart()
{
glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();
gluOrtho2D(-w1/2, w1/2, -h1/2, h1/2);
glMatrixMode(GL_MODELVIEW);
}
void orthogonalEnd()
{
glMatrixMode(GL_PROJECTION);
glPopMatrix();
glMatrixMode(GL_MODELVIEW);
}
GLuint texture = 0;
void background()
{
glBindTexture( GL_TEXTURE_2D, texture );
orthogonalStart();
// texture width/height
const int iw = 500;
const int ih = 500;
glPushMatrix();
glTranslatef( -iw/2, -ih/2, 0 );
glBegin(GL_QUADS);
glTexCoord2i(0,0); glVertex2i(0, 0);
glTexCoord2i(1,0); glVertex2i(iw, 0);
glTexCoord2i(1,1); glVertex2i(iw, ih);
glTexCoord2i(0,1); glVertex2i(0, ih);
glEnd();
glPopMatrix();
orthogonalEnd();
}
void display()
{
glClearColor (1.0,0.0,0.0,1.0);
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glEnable( GL_TEXTURE_2D );
background();
gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
glutSwapBuffers();
}
GLuint LoadTexture()
{
unsigned char data[] = { 255,0,0, 0,255,0, 0,0,255, 255,255,255 };
glGenTextures( 1, &texture );
glBindTexture( GL_TEXTURE_2D, texture );
glPixelStorei( GL_UNPACK_ALIGNMENT, 1 );
glTexEnvf( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE );
//even better quality, but this will do for now.
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,GL_NEAREST);
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,GL_NEAREST);
//to the edge of our shape.
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT );
//Generate the texture
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 2, 2, 0,GL_RGB, GL_UNSIGNED_BYTE, data);
return texture; //return whether it was successful
}
int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE);
glutInitWindowSize(800,600);
glutCreateWindow("Aspect Ratio");
glutDisplayFunc(display);
glutReshapeFunc(reshape);
texture = LoadTexture();
glutMainLoop();
return 0;
}
Vitalij
A full time software engineer working for M&S. I am also an entrepreneur.
Updated on July 17, 2022Comments
-
Vitalij almost 2 years
I am trying to set a background image of my openGL window by creating a quad on an orthogonal projection matrix and adding texture to it. I am also making use of GLUT toolkit in my application.
However I am having several problems. Below are screenshot illustrating the problem: image is grayscale and it repeats on x and y, even though texture size is set to be the same as the quad.
That is what I am trying to achieve:
And that is what I am getting:
Code for rendering and loading texture looks like this:
void orthogonalStart (void) { glMatrixMode(GL_PROJECTION); glPushMatrix(); glLoadIdentity(); gluOrtho2D(0, w1, 0, h1); glScalef(1, -1, 1); glTranslatef(0, -h1, 0); glMatrixMode(GL_MODELVIEW); } void orthogonalEnd (void) { glMatrixMode(GL_PROJECTION); glPopMatrix(); glMatrixMode(GL_MODELVIEW); } GLuint LoadTexture( const char * filename, int width, int height ) { GLuint texture; unsigned char * data; FILE * file; //The following code will read in our RAW file file = fopen( filename, "rb" ); if ( file == NULL ) return 0; data = (unsigned char *)malloc( width * height * 3 ); fread( data, width * height * 3, 1, file ); fclose( file ); glGenTextures( 1, &texture ); glBindTexture( GL_TEXTURE_2D, texture ); glTexEnvf( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE ); //even better quality, but this will do for now. glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,GL_LINEAR ); glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,GL_LINEAR ); //to the edge of our shape. glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT ); glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT ); //Generate the texture glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0,GL_RGB, GL_UNSIGNED_BYTE, data); free( data ); //free the texture return texture; //return whether it was successful } void FreeTexture( GLuint texture ) { glDeleteTextures( 1, &texture ); } void background (void) { glBindTexture( GL_TEXTURE_2D, texture ); orthogonalStart(); glBegin(GL_QUADS); glTexCoord2d(0.0,0.0); glVertex2f(0, 0); glTexCoord2d(1.0,0.0); glVertex2f(1024, 0); glTexCoord2d(1.0,1.0); glVertex2f(1024, 1024); glTexCoord2d(0.0,1.0); glVertex2f(0, 1024); glEnd(); orthogonalEnd(); } void display (void) { glClearColor (1.0,0.0,0.0,1.0); glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glLoadIdentity(); glEnable( GL_TEXTURE_2D ); background(); gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0); glutSwapBuffers(); }
To convert texture from png into Raw format I use photoshop, so I thought greyscale image might be due to conversion.
Note: I have just started learning open, so this might be not the best approach. Please let me know if there is a better way
Edit: Image has to stay on one place and not rescalse