Question

I am trying to write code that will cycle between rendering an animation and rendering a heads up display. The animation works, however I am having difficulty switching between the animation’s projection matrix and another orthographic projection matrix for the HUD.

The main loop runs as follows:

init();
while (isAnimationRunning) {
    drawAnimation();
    drawHUD();
}

And the initialization of the surface is:

void init(){
    glEnableClientState(GL10.GL_VERTEX_ARRAY);
    glClearColor(1, 1, 1, 1);
    glMatrixMode(GL11.GL_PROJECTION);
    glLoadIdentity();
    glViewport(0, 0, windowWidth, windowHeight);
    GLU.gluPerspective(gl11, 45.0f, windowWidth / windowHeight, 0.1f, 100.0f);
}

And the code for the animation rendering

void drawAnimation() {
        glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT);
        glMatrixMode(GL10.GL_MODELVIEW);
        glLoadIdentity();
        GLU.gluLookAt(gl11, x, y, zoom, x, y, 0, 0, 1, 0);
            drawAnimationTextures();
}

And the code for the HUD rendering

void drawHUD(){
        glMatrixMode(GL10.GL_MODELVIEW);
        glPushMatrix();

            // IF THIS LINE IS REMOVED THE ANIMATION DISPLAYS BUT NOT THE HUD
        glLoadIdentity(); 

        glClear(GL10.GL_COLOR_BUFFER_BIT);
        GLU.gluLookAt(gl11, 0, 0, 2, 0, 0, 0, 0, 1, 0);

        glMatrixMode(GL10.GL_PROJECTION);
        glPushMatrix();
        glLoadIdentity();
        GLU.gluPerspective(gl11, 45, aspectRatio, 0.1f, 100.0f);
        glOrthof(-aspectRatio, aspectRatio, -1, 1, -4, 4);

        drawHUDTexture();

    glPopMatrix();
        glMatrixMode(GL10.GL_MODELVIEW);
        glPopMatrix();
}

The screen is blank when this code is implemented. Any ideas what the problem might be?

////////////////////////

void drawTexture(float x, float y, float z, float sizeX, float sizeY,...){
            glEnable(GL10.GL_TEXTURE_2D);
            glPushMatrix();
            bindTexture(texture);
            glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
            glFrontFace(GL10.GL_CW);
            glColor4f(RGB[0], RGB[1], RGB[2], alpha);
            glTranslatef(x, y, z);
            glScalef(sizeX, sizeY, sizeZ);
            glVertexPointer(3, GL10.GL_FLOAT, 0, squareVertexBuffer);
            glTexCoordPointer(2, GL10.GL_FLOAT, 0, textureBuffer);
            glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, 4);
            glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
            glPopMatrix();
}

Answer 1

Why are you clearing the framebuffer in both routines? You should call it once only in your top level loop. If the animation appears when you comment out the loadidentity but still have the glclear there I am puzzled.

It looks like the hud overwrites the whole screen, make it semi transparent to check this, it may be so large you’re just seeing a small part of it.

plus your hud code is setting up a perspective view, then an ortho view – which one do you want?