Question

Would anyone share an example on how to implement GradienRectangle that would have different colors for each vertex?

I’ve tried to call glColorPointer from GL10 passing float buffer and GL11 using similar to vertices selectOnHardware approach but both methods failed for me…

On AndEngine forum I found this code, but it does not work, however maby it will help someone to find a better solution.

Answer 1

that example does not work for you because author have not shown piece of code responsible for setting vertexes.

Here is my example(it is long, but that’s opengl…)
NOTE – remember to setUp viewport correctly.

public static void drawGradientRectangle(GL10 gl, float centerX, float centerY,
            float width, float height) {
        gl.glPushMatrix();
        gl.glDisable(GL10.GL_TEXTURE_2D);
        gl.glEnableClientState(GL10.GL_COLOR_ARRAY);
        gl.glEnableClientState(GL10.GL_VERTEX_ARRAY); //just in case if you have not done that before
        gl.glFrontFace(GL10.GL_CCW); //Set the face

        gl.glTranslatef(centerX, centerY, 0);
        if (width != 1 || height != 1) {
            gl.glScalef(width, height, 1);
        }
        gl.glVertexPointer(2, GL10.GL_FLOAT, 0, GLDrawConstants.vertexBuffer0_5);
        gl.glColorPointer(4, GL10.GL_FLOAT, 0, GLDrawConstants.gradOrangeWhiteBuffer);

        // Draw the vertices as triangle strip
        gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, 4);

        gl.glDisableClientState(GL10.GL_COLOR_ARRAY);
        gl.glEnable(GL10.GL_TEXTURE_2D);
        gl.glPopMatrix();
    }

GLDrawConstants class:

public class GLDrawConstants {

    public static final FloatBuffer gradOrangeWhiteBuffer;
    public static final FloatBuffer vertexBuffer0_5;

private static final float vertices0_5[] = { 
        -0.5f, -0.5f,// Bottom Left
        0.5f, -0.5f,// Bottom right
        -0.5f, 0.5f,// Top Left
        0.5f, 0.5f// Top Right
    };

private static final float gradOrangeWhiteColor[] = {
        255/255f, 239/255f, 196/255f, 0f, // Bottom Left 
        255/255f, 239/255f, 196/255f, 0f, // Bottom right
        250/255f, 200/255f, 62/255f, 0.3f, // Top Left
        250/255f, 200/255f, 62/255f, 0.3f  // Top Right
    };

static {
        gradOrangeWhiteBuffer = WDUtils.floatBuffer(gradOrangeWhiteColor);
        vertexBuffer0_5 = WDUtils.floatBuffer(vertices0_5);
}

}

WDUtils class:

public class WDUtils {
    /**
     * Make a direct NIO FloatBuffer from an array of floats
     * 
     * @param arr
     *            The array
     * @return The newly created FloatBuffer
     */
    public static final FloatBuffer floatBuffer(float[] arr) {
        ByteBuffer bb = ByteBuffer.allocateDirect(arr.length * 4);
        bb.order(ByteOrder.nativeOrder());
        FloatBuffer fb = bb.asFloatBuffer();
        fb.put(arr);
        fb.position(0);
        return fb;
    }
}