Peter B. Peter B. - 12 days ago 5
C Question

How to switch between textures/framebuffers on keypress using GLUT?

I have two buffers with

.rgb
images loaded. Original image is stored in
frame_buffer
and second one is stored in
temp_buffer
. I want to switch between those two images in GLUT window, when user press a button, how can I extend my code to do this?

typedef struct pixel{
GLbyte r;
GLbyte g;
GLbyte b;
}Pixel;

Pixel frame_buffer[WIDTH][HEIGHT]; //original image
Pixel temp_buffer[WIDTH][HEIGHT]; //embossed image

GLuint texture;

int window_id;


void keyboardFunction(unsigned char button, int x, int y){
switch(button){
case 'S':
case 's':
// WHEN USER PRESS 'S', NEW IMAGE FROM temp_buffer IS
// LOADED, HOW CAN I DO THIS?
break;
default:
break;
}
glutPostRedisplay();
}


// Initialize OpenGL state
void init() {
// Texture setup
glEnable(GL_TEXTURE_2D);
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);

// Other
glClearColor(0, 0, 0, 0);
gluOrtho2D(-1, 1, -1, 1);
glLoadIdentity();
glColor3f(1, 1, 1);

loadInputFromUser();
emboss();
}


void display() {
// Copy frame_buffer to texture memory
glBindTexture(GL_TEXTURE_2D, texture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, WIDTH, HEIGHT, 0, GL_RGB, GL_UNSIGNED_BYTE, frame_buffer);
// Clear screen buffer
glClear(GL_COLOR_BUFFER_BIT);
// Render a quad
glBegin(GL_QUADS);
glTexCoord2f(1, 0); glVertex2f(1, 1);
glTexCoord2f(1, 1); glVertex2f(1, -1);
glTexCoord2f(0, 1); glVertex2f(-1, -1);
glTexCoord2f(0, 0); glVertex2f(-1, 1);
glEnd();
// Display result
glFlush();
//glutPostRedisplay();
glutSwapBuffers();
}


// Main entry function
int main(int argc, char **argv) {

// Init GLUT
glutInit(&argc, argv);
glutInitWindowPosition(-1, -1);
glutInitWindowSize(WIDTH, HEIGHT);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutCreateWindow("Convolution Filter");
// Set up OpenGL state
init();
// Run the control loop
glutDisplayFunc(display);
glutKeyboardFunc(keyboardFunction);
glutReshapeFunc(changeViewPoint);

GLenum err = glewInit();
if (GLEW_OK != err){
fprintf(stderr, "GLEW error");
return 1;
}
glutMainLoop();
return EXIT_SUCCESS;
}



  1. original image stored in
    frame_buffer


    enter image description here


  2. image filtered with emboss stored in
    temp_buffer
    (yeah I know its not perfect :D )

    enter image description here




I want to switch between them with keybutton.

Answer

Edit the following snippets:

Pixel frame_buffer[WIDTH][HEIGHT]; //original image
Pixel temp_buffer[WIDTH][HEIGHT]; //embossed image
int which_image = 0;

...

    case 'S':
    case 's':
        which_image ^= 1;
        break;

...

glBindTexture(GL_TEXTURE_2D, texture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, WIDTH, HEIGHT, 0, GL_RGB, GL_UNSIGNED_BYTE, which_image == 0 ? frame_buffer : temp_buffer);

...

glFlush();
glutPostRedisplay();
glutSwapBuffers();

That being said, you currently upload the texture (glTexImage2D) for each frame drawn. You should rather upload it only once during startup and each time it changes.

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