Simple OpenGL Texture Example

Here is a simple example of code to use an OpenGL Texture.

// Apple gcc program0.c -framework opengl -framework glut
// A simple OpenGL and glut program 
#include <GLUT/glut.h> /* Header File For The GLut Library*/
#include <stdint.h>

//
// You need to generate the texture data that you are going to
// use. GIMP will convert a bitmap, jpg, etc. to a "C" structure
// that you can use almost directly.
//


// GIMP RGBA C-Source image dump (f35_schem_02_edit_4.c) 

static const struct {
  uint32_t     width;
  uint32_t     height;
  uint32_t     bytes_per_pixel; /* 3:RGB, 4:RGBA */
  uint8_t      pixel_data[128 * 128 * 4 + 1];
} planform = {
  128, 128, 4,
  "\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0"
  "\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0"
  "\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0"
  "\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377"
  // ... much of the texture deleted
  "\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0"
  "\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377\0\0\0\377",
};


// The routine to draw the screen
void display() { 
    // A value to hold our texture handle
    static uint32_t texture = 0;
    static int32_t  firstTimeDone = 0;

    // Clear the display
    glClear(GL_COLOR_BUFFER_BIT); 
    // Set the color to white
    glColor3f(1.0, 1.0, 1.0);
    // Setup the coordinates to what I am used to
    glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0); 

    // Get a texture number if we dont have one
    if (!firstTimeDone)
    {
        // Get a texture number
        glGenTextures(1, &texture);

        // Tell OpenGL that we want to use that texture
        glBindTexture(GL_TEXTURE_2D, texture);

        // You have to tell OpenGL how to take the raw bitmap data
        // in the structure above to put it into a texture. We
        // do this with a glTexImage2D() call. We will describe the
        // structure above and how we want it stored internally in 
        // OpenGl.
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, planform.width, planform.height, 
            0, GL_RGBA, GL_UNSIGNED_BYTE, planform.pixel_data);

        // OpenGl lets you describe how you want to scale the 
        // texture data when the destination is bigger or smaller
        // than the original texture data. In this case, we want
        // simple linear scaling.
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

        // First Time is done
        firstTimeDone = 1;
    }
    else
    {
        // Tell OpenGL that we want to use that texture
        glBindTexture(GL_TEXTURE_2D, texture);
    }

    // We are going to put the texture on a 2D surface, much
    // like we would apply a decal.
    glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);

    // Normally you leave GL_TEXTURE_2D turned off unless 
    // you are applying a decal to a surface. Since we are
    // doing that, we turn it on here.
    glEnable(GL_TEXTURE_2D);

    // Draw the square
    glBegin(GL_POLYGON);

    // Here we want to associate a point in the texture with the
    // vertex we are drawing on the screen. So these are paired up.
    glTexCoord2f(0.0f, 1.0f); glVertex2f(-0.5, -0.5);
    glTexCoord2f(0.0f, 0.0f); glVertex2f(-0.5, 0.5);
    glTexCoord2f(1.0f, 0.0f); glVertex2f(0.5, 0.5);
    glTexCoord2f(1.0f, 1.0f); glVertex2f(0.5, -0.5);

    // End of the list of verticies
    glEnd();
    // Turn texture drawing back off, normally we leave if off.
    glDisable(GL_TEXTURE_2D);

    // Flush the data. In many drivers, this causes the
    // actual draw to the Frame Buffer.
    glFlush();
} 

int main(int argc, char **argv) { 
    // A minimal GLUT setup to get GLUT up and going.
    // If you use EGL or some other windowing system
    // other than GLUT, you need to replace this.
    glutInit(&argc, argv); 
    glutInitWindowSize(512,512); 
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); 
    glutCreateWindow("The glut hello world program"); 
    glutDisplayFunc(display); 
    glClearColor(0.0, 0.0, 0.0, 1.0); 
    glutMainLoop(); // Infinite event loop 
    return 0; 
} 

</stdint.h>