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java – Using OpenGL to replace Canvas – Android

Posted by: admin June 15, 2020 Leave a comment

Questions:

I am attempting to replace the Canvas-based rendering system that I already have with the faster opengl-es surface, however, I can’t seem to get an openGL renderer to conform in such a way that it acts as 2d field, rather than a perspective view.

My current code for the renderer looks as follows:

     @Override
     public void onSurfaceChanged(GL10 gl, int width, int height) {
        gl.glViewport(0, 0, width, height);
        gl.glMatrixMode(GL10.GL_PROJECTION);
        gl.glLoadIdentity();
        gl.glOrthof(0.0f, width, 0.0f, height, 0.0f, 1.0f);

        gl.glShadeModel(GL10.GL_FLAT);
        gl.glEnable(GL10.GL_BLEND);
        gl.glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA);
        gl.glColor4x(0x10000, 0x10000, 0x10000, 0x10000);
        gl.glEnable(GL10.GL_TEXTURE_2D);
    }

    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig config) {
        gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT, GL10.GL_FASTEST);

        gl.glClearColor(0.5f, 0.5f, 0.5f, 1);
        gl.glShadeModel(GL10.GL_FLAT);
        gl.glDisable(GL10.GL_DEPTH_TEST);
        gl.glEnable(GL10.GL_TEXTURE_2D);

        gl.glDisable(GL10.GL_DITHER);
        gl.glDisable(GL10.GL_LIGHTING);

        gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);    
    }

How would I setup the renderer so that the translate transformation would match up with the pixels on the screen? (so translating 5 to the right would move it 5 pixels)

How to&Answers:

Please note that in openGL that Y co-ordinate is inverted. Otherwise all is the same.
As for the correct flags, I recommend you check out the open source android game replica island: http://code.google.com/p/replicaisland/

Here’s what I use in my own code:

public void onSurfaceChanged(GL10 gl, int width, int height) 
{
    mViewWidth = width;
    mViewHeight = height;

    gl.glViewport(0, 0, mViewWidth,  mViewHeight);
    gl.glLoadIdentity();
    GLU.gluOrtho2D(gl, 0, mViewWidth, mViewHeight, 0);
}

public void onSurfaceCreated(GL10 gl, EGLConfig config) 
{
    gl.glClearColor(0.5f, 0.5f, 0.5f, 1);
    gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT, GL10.GL_FASTEST);
    gl.glShadeModel(GL10.GL_FLAT);
    gl.glDisable(GL10.GL_DEPTH_TEST);
    gl.glEnable(GL10.GL_BLEND);
    gl.glBlendFunc(GL10.GL_ONE, GL10.GL_ONE_MINUS_SRC_ALPHA); 

    gl.glViewport(0, 0, mViewWidth,  mViewHeight);
    gl.glMatrixMode(GL10.GL_PROJECTION);
    gl.glLoadIdentity();
    gl.glEnable(GL10.GL_BLEND);
    gl.glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA);
    gl.glShadeModel(GL10.GL_FLAT);
    gl.glEnable(GL10.GL_TEXTURE_2D);

    GLU.gluOrtho2D(gl, 0, mViewWidth, mViewHeight, 0);
}

Where mViewWidth & mViewHeight are the size of the display.