Are OpenGL polygons stuck in the upper left?

Question

I use theallegro library and through it OpenGL. I turn on depth testing, and then when resizing:

    glEnable(GL_CULL_FACE);
    glCullFace(GL_BACK);
    glEnable(GL_DEPTH_TEST);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glFrustum(0,event.display.width,event.display.height,0,1,300);

Then my drawing looks like this:

float BOX_SIZE = 200.0f;
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);


        glRotatef(0.5, 0, 0.0f, 1.0f);
        glBegin(GL_QUADS);

        //Top face
        glColor3f(1.0f, 1.0f, 0.0f);
        glNormal3f(0.0, 1.0f, 0.0f);
        glVertex3f(500 + -BOX_SIZE / 2, BOX_SIZE / 2, -BOX_SIZE / 2);
        glVertex3f(500 + -BOX_SIZE / 2, BOX_SIZE / 2, BOX_SIZE / 2);
        glVertex3f(500 + BOX_SIZE / 2, BOX_SIZE / 2, BOX_SIZE / 2);
        glVertex3f(500 + BOX_SIZE / 2, BOX_SIZE / 2, -BOX_SIZE / 2);

        //Bottom face
        glColor3f(1.0f, 0.0f, 1.0f);
        glNormal3f(0.0, -1.0f, 0.0f);
        glVertex3f(-BOX_SIZE / 2, -BOX_SIZE / 2, -BOX_SIZE / 2);
        glVertex3f(BOX_SIZE / 2, -BOX_SIZE / 2, -BOX_SIZE / 2);
        glVertex3f(BOX_SIZE / 2, -BOX_SIZE / 2, BOX_SIZE / 2);
        glVertex3f(-BOX_SIZE / 2, -BOX_SIZE / 2, BOX_SIZE / 2);

        //Left face
        glNormal3f(-1.0, 0.0f, 0.0f);
        glColor3f(0.0f, 1.0f, 1.0f);
        glVertex3f(-BOX_SIZE / 2, -BOX_SIZE / 2, -BOX_SIZE / 2);
        glVertex3f(-BOX_SIZE / 2, -BOX_SIZE / 2, BOX_SIZE / 2);
        glColor3f(0.0f, 0.0f, 1.0f);
        glVertex3f(-BOX_SIZE / 2, BOX_SIZE / 2, BOX_SIZE / 2);
        glVertex3f(-BOX_SIZE / 2, BOX_SIZE / 2, -BOX_SIZE / 2);

        //Right face
        glNormal3f(1.0, 0.0f, 0.0f);
        glColor3f(1.0f, 0.0f, 0.0f);
        glVertex3f(BOX_SIZE / 2, -BOX_SIZE / 2, -BOX_SIZE / 2);
        glVertex3f(BOX_SIZE / 2, BOX_SIZE / 2, -BOX_SIZE / 2);
        glColor3f(0.0f, 1.0f, 0.0f);
        glVertex3f(BOX_SIZE / 2, BOX_SIZE / 2, BOX_SIZE / 2);
        glVertex3f(BOX_SIZE / 2, -BOX_SIZE / 2, BOX_SIZE / 2);

        glEnd();

        glEnable(GL_TEXTURE_2D);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glColor3f(1.0f, 1.0f, 1.0f);
        glBegin(GL_QUADS);

        //Front face
        glNormal3f(0.0, 0.0f, 1.0f);
        glTexCoord2f(0.0f, 0.0f);
        glVertex3f(-BOX_SIZE / 2, -BOX_SIZE / 2, BOX_SIZE / 2);
        glTexCoord2f(1.0f, 0.0f);
        glVertex3f(BOX_SIZE / 2, -BOX_SIZE / 2, BOX_SIZE / 2);
        glTexCoord2f(1.0f, 1.0f);
        glVertex3f(BOX_SIZE / 2, BOX_SIZE / 2, BOX_SIZE / 2);
        glTexCoord2f(0.0f, 1.0f);
        glVertex3f(-BOX_SIZE / 2, BOX_SIZE / 2, BOX_SIZE / 2);

        //Back face
        glNormal3f(0.0, 0.0f, -1.0f);
        glTexCoord2f(0.0f, 0.0f);
        glVertex3f(-BOX_SIZE / 2, -BOX_SIZE / 2, -BOX_SIZE / 2);
        glTexCoord2f(1.0f, 0.0f);
        glVertex3f(-BOX_SIZE / 2, BOX_SIZE / 2, -BOX_SIZE / 2);
        glTexCoord2f(1.0f, 1.0f);
        glVertex3f(BOX_SIZE / 2, BOX_SIZE / 2, -BOX_SIZE / 2);
        glTexCoord2f(0.0f, 1.0f);
        glVertex3f(BOX_SIZE / 2, -BOX_SIZE / 2, -BOX_SIZE / 2);

        glEnd();
        glDisable(GL_TEXTURE_2D);
 //code goes here
 al_flip_display();

for some reason the cube no matter how i translated it seems to extend from 0.0, and theres always a vertex of 0.0. What have I done wrong? Thanks

Answer 1

I don’t know any features of the allegro library, but when reading a piece of code, two things come to mind.

• Why don't you call glViewport(event.display.width,event.display.height) when resizing? The glFrustum request should usually not depend on the size of the display.

• - glMatrixMode(GL_MODELVIEW)? .

, .