Question

I’m getting some strange values for the width/height in the following code, resulting in either a stretched picture, or no picture at all.

public void onSurfaceChanged(GL10 gl, int w, int h) {

    screenHeight = h;  // actual height in pixels
    screenWidth = w;   // actual width in pixels
    worldWidth = 20;   // width of the projection (20 units)
    worldHeight = (int) (worldWidth * (screenHeight / screenWidth));  

    gl.glMatrixMode(GL10.GL_PROJECTION);
    gl.glViewport(0, 0, screenWidth, screenHeight); //new viewport
    gl.glLoadIdentity();
    GLU.gluOrtho2D(gl, 0, worldWidth, 0, worldHeight); set the 2D projection  

So I logged the variables, these are from portrait mode:

screenHeight = 455  
screenWidth = 320  
worldHeight = 20  
worldWidth = 20    

while (worldWidth * (screenHeight / screenWidth) should give 20*455/320=28 for worldHeight.

It gets even stranger in landscape mode, where worldHeight suddenly equals 0.

What am I doing wrong?

Answer 1

Let me guess, screenHeight and screenWidth are both ints? In this case the division will be an integer division, resulting in a rounded/truncated integer and therefore being 0 if the ratio is <1. Cast at least one of the operands of the division to a floating point number to perform a real floating point division:

worldHeight = (int) (worldWidth * ((float)screenHeight / (float)screenWidth));