CODEWITHSUNDEEP
androidopengl-es
toom
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Reputation: 61

OpenGL inversion in y-axis

I'm using the OpenGL touch events to move shapes but what happens is the shapes on the opposite side of the screen move (x-axis). So if you try to move a shape at the bottom, then a shape at the top will move inside. The top right corner is (0,480) and the bottom left (800,0). I've tried changing the numbers round inthe view matrix but it hasnt worked. Why is this happening?

Im sure I've set my view and projection matrices correctly. Here they are.

@Override
    public void onSurfaceCreated(GL10 unused, EGLConfig config) {

        // Set the background clear color to gray.
        GLES20.glClearColor(0.5f, 0.5f, 0.5f, 0.5f);

        GLES20.glFrontFace(GLES20.GL_CCW); // Counter-clockwise winding.
        GLES20.glEnable(GLES20.GL_CULL_FACE);// Use culling to remove back faces.
        GLES20.glCullFace(GLES20.GL_BACK);// What faces to remove with the face culling.
        GLES20.glEnable(GLES20.GL_DEPTH_TEST);// Enable depth testing

        // Position the eye behind the origin.
        final float eyeX = 0.0f;
        final float eyeY = 0.0f;
        final float eyeZ = -3.0f;

        // We are looking toward the distance
        final float lookX = 0.0f;
        final float lookY = 0.0f;
        final float lookZ = 0.0f;

        // Set our up vector. This is where our head would be pointing were we holding the camera.
        final float upX = 0.0f;
        final float upY = 1.0f;
        final float upZ = 0.0f;

        Matrix.setLookAtM(mViewMatrix, 0, eyeX, eyeY, eyeZ, lookX, lookY, lookZ, upX, upY, upZ);
        Matrix.setIdentityM(mViewMatrix, 0);

    }

    @Override
    public void onSurfaceChanged(GL10 unused, int width, int height) {
        // Sets the current view port to the new size.
        GLES20.glViewport(0, 0, width, height);

        float RATIO = (float) width / (float) height;

        // this projection matrix is applied to object coordinates in the onDrawFrame() method
        Matrix.frustumM(mProjectionMatrix, 0, -RATIO, RATIO, -1, 1, 1, 10);
        Matrix.setIdentityM(mProjectionMatrix, 0);
    }

Update

The view seems to render properly. And the shape will appear on the screen where i want them to, if i translate them, or change the vertex coordinates slightly. Whats not right is how it registers the touch events. Any ideas?

This is how i check the touch events.

if(shapeW < minX){minX = shapeW;}
                if(shapeW > maxX){maxX = shapeW;}
                if(shapeH < minY){minY = shapeH;}
                if(shapeH > maxY){maxY = shapeH;}

                //Log.i("Min&Max" + (i / 4), String.valueOf(minX + ", " + maxX + ", " + minY + ", " + maxY));

                if(minX < MyGLSurfaceView.touchedX && MyGLSurfaceView.touchedX < maxX && minY < MyGLSurfaceView.touchedY && MyGLSurfaceView.touchedY < maxY)
                {
                    xAng[j] = xAngle;
                    yAng[j] = yAngle;
                    Log.i("cube "+j, " pressed");
                   }

Upvotes: 1

Views: 480

Answers (1)

NigelK
NigelK

Reputation: 8455

From the origin, the z-axis is positive coming towards you and negative going away into the screen. So if my assumption is correct that your shapes are drawn in the z = 0 plane, your eye is actually positioned behind them. Hence if you move an object one way it appears to move the other way. Try using a positive value for eyeZ instead.

For example, eye = (0, 0, 3), look = (0, 0, 0) would position the eye out of the origin towards you looking down into the screen. In contrast, using eye = (0, 0, -3), look = (0, 0, 0) would put the eye into the screen looking back out of it.

Upvotes: 1

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