Using multiple viewports

souza · by **souza** » Fri Aug 20, 2010 9:59 pm

Hi,

I'm trying to get two viewports setup on the screen of the Android Emulator. The FIRST VIEWPORT (orthographic projection) fills the emulators screen and displays a white, screen filling polygon. The SECOND VIEWPORT (perspective projection) is only a square inside the screen and should appear above the other viewport showing a cube. Now, when i have both viewports active I cannot see the white polygon but the smaller viewport with the cube. In case I have the second viewports code in block comments it again apears. I don't get where I have to modify the code that both viewport appear correctly on the emulator. Here are some code snippets:

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public void onSurfaceCreated(GL10 gl, EGLConfig config) {
                // Set the background color to red ( rgba ).
                gl.glClearColor(1.0f, 0.0f, 0.0f, 0.5f);
                // Enable Smooth Shading, default not really needed.
                gl.glShadeModel(GL10.GL_SMOOTH);
                // Depth buffer setup.
                gl.glClearDepthf(1.0f);
                // Enables depth testing.
                gl.glEnable(GL10.GL_DEPTH_TEST);
                // The type of depth testing to do.
                gl.glDepthFunc(GL10.GL_LEQUAL);
                // Really nice perspective calculations.
                gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT, GL10.GL_NICEST);
}
 
public void onDrawFrame(GL10 gl) {              
                
                // Clears the screen and depth buffer.
                gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
                // Modelview Matrix selektieren
                gl.glMatrixMode(GL10.GL_MODELVIEW);
                // Replace the current Matrix with the identity matrix
                gl.glLoadIdentity();
                // Translates 6 units into the screen
                gl.glTranslatef(0, 0, -10);
                
                // Draw RECTANGLE
                square.draw(gl);
        
                // CUBE
                // Save the current matrix
                gl.glPushMatrix();
                        gl.glTranslatef(0, 0, -5);
                        // Draw the cube
                        root.draw(gl);
                // Restore the last matrix
                gl.glPopMatrix();
}
 
public void onSurfaceChanged(GL10 gl, int width, int height) {
                
                for(int i = 0; i < 2; i++) {
                        
                        if(i==0) {
                                // Main Viewport
                                gl.glViewport(0, 0, width, height);
                                // Select the projection matrix
                                gl.glMatrixMode(GL10.GL_PROJECTION);
                                // Reset the projection matrix
                                gl.glLoadIdentity();
                                // Setup orthographic projection. Consider aspect ratio to avoid distortion.
                                if(width < height) {
                                        gl.glOrthof(-1.0f, 1.0f, -1.0f * height / width, 1.0f * height / width, -2.0f, 10.0f);
                                } else {
                                        gl.glOrthof(-1.0f * width / height, 1.0f * width / height, -1.0f, 1.0f, -2.0f, 10.0f);
                                }
                                
                                GLU.gluLookAt(gl, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, -1.0f, 0.0f, 1.0f, 0.0f);                               
                        }
                        
                        if(i==1) {
                                // Sets the cube's viewport.
                                gl.glViewport(width/2, height/3, width/2, height/3);
                                // Select the projection matrix
                                gl.glMatrixMode(GL10.GL_PROJECTION);
                                // Reset the projection matrix
                                gl.glLoadIdentity();
                                // Calculate the aspect ratio of the window
                                GLU.gluPerspective(gl, 45.0f, (float) width / (float) height, -2.0f, 10.0f);
                                
                                GLU.gluLookAt(gl, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, -1.0f, 0.0f, 1.0f, 0.0f);
                        }
                        // Select the modelview matrix
                        gl.glMatrixMode(GL10.GL_MODELVIEW);
                        // Reset the modelview matrix
                        gl.glLoadIdentity();
                        // Clear Depth Buffer
                        gl.glClear(GL10.GL_DEPTH_BUFFER_BIT);
                }
}
 
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That's how it looks like without the FIRST VIEWPORT:

MichaelEGR · by **MichaelEGR** » Sun Aug 22, 2010 3:18 pm

As things go I don't have time to look at your code, but just offer this word of advice.. Don't try this kind of thing in the emulator as you'll just run into problems if not with this particular use case then something you try soon enough just simply will not work in the emulator because it is of very poor quality for OpenGL ES support. It's a rule of thumb that you just got to try OpenGL ES efforts out on a real device. So move to a real device as soon as possible.

souza · by **souza** » Sun Aug 22, 2010 3:51 pm

My problem is that I am working on a tablet PC with Windows 7 and didn't get a real android device from my university :S So I'm more or less forced to keep going with the emulator!

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