Adding colors with OpenGL ES in Android

In the post Drawing a triangle with OpenGL ES in Android I explained how to draw a triangle without setting the colors, indeed, the triangle is gray.
In this post I add a few lines of code that allow you to change the color of the triangle starting from the code in Drawing a triangle with OpenGL ES in Android.

You can edit the same project created in Drawing a triangle with OpenGL ES in Android or create a new one and follow its first 3 steps.

1. edit the file eu/lucazanini/opengl/shape/ShapeRenderer.java

   package eu.lucazanini.opengl.shape;
   
   import javax.microedition.khronos.egl.EGLConfig;
   import javax.microedition.khronos.opengles.GL10;
   import javax.microedition.khronos.opengles.GL11;
   
   import android.opengl.GLSurfaceView;
   
   public class ShapeRenderer implements GLSurfaceView.Renderer {
   
       private Triangle shape;
   
       public ShapeRenderer() {
   	shape = new Triangle();
       }
   
       @Override
       public void onDrawFrame(GL10 gl) {
   
   	gl.glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT);
   
   	gl.glMatrixMode(GL11.GL_MODELVIEW);
   	gl.glLoadIdentity();
   
   	// gl.glTranslatef(1.0f, 0.0f, 0.0f);
   	// gl.glRotatef(90.0f, 0.0f, 0.0f, 1.0f);
   
   	gl.glEnableClientState(GL11.GL_VERTEX_ARRAY);
   	gl.glEnableClientState(GL11.GL_COLOR_ARRAY);
   
   	shape.draw(gl);
   
   	gl.glDisableClientState(GL11.GL_VERTEX_ARRAY);
   	gl.glDisableClientState(GL11.GL_COLOR_ARRAY
       }
   
       @Override
       public void onSurfaceChanged(GL10 gl, int width, int height) {
   
   	gl.glViewport(0, 0, width, height);
   
   	float ratio;
   	float zNear = .1f;
   	float zFar = 1000f;
   	float fieldOfView = (float) Math.toRadians(30);
   	float size;
   
   	gl.glEnable(GL11.GL_NORMALIZE);
   
   	ratio = (float) width / (float) height;
   
   	gl.glMatrixMode(GL11.GL_PROJECTION);
   
   	size = zNear * (float) (Math.tan((double) (fieldOfView / 2.0f)));
   
   	gl.glFrustumf(-size, size, -size / ratio, size / ratio, zNear, zFar);
   
   	gl.glMatrixMode(GL11.GL_MODELVIEW);
       }
   
       @Override
       public void onSurfaceCreated(GL10 gl, EGLConfig config) {
   
   	gl.glDisable(GL11.GL_DITHER);
   
   	gl.glHint(GL11.GL_PERSPECTIVE_CORRECTION_HINT, GL11.GL_FASTEST);
   
   	gl.glClearColor(0, 0, 0, 0);
   
   	gl.glEnable(GL11.GL_CULL_FACE);
   	gl.glFrontFace(GL11.GL_CCW);
   
   	gl.glShadeModel(GL11.GL_SMOOTH);
   
   	gl.glEnable(GL11.GL_DEPTH_TEST);
       }
   
   }
   

   the only difference with Drawing a triangle with OpenGL ES in Android is the lines 29 and 34

2. edit the file eu/lucazanini/opengl/shape/Triangle.java

   package eu.lucazanini.opengl.shape;
   
   import java.nio.ByteBuffer;
   import java.nio.ByteOrder;
   import java.nio.FloatBuffer;
   
   import javax.microedition.khronos.opengles.GL10;
   import javax.microedition.khronos.opengles.GL11;
   
   public class Triangle {
   
       private FloatBuffer mFVertexBuffer;
       private ByteBuffer mIndexBuffer;
       private FloatBuffer mColorBuffer;
   
       public Triangle() {
   
   	float vertices[] = {
   		-0.5f, -0.29f, -10f, 
   		0.5f, -0.29f, -10f, 
   		0f, 0.58f, -10f 
       }; 
   
   	byte indices[] = { 0, 1, 2 };
   	
   	float colors[] = {
   	 1, 0, 0, 1, 
   		0, 1, 0, 1, 
   		0, 0, 1, 1 
   	};
   
   	mFVertexBuffer = makeFloatBuffer(vertices);
   
   	mIndexBuffer = ByteBuffer.allocateDirect(indices.length);
   	mIndexBuffer.put(indices);
   	mIndexBuffer.position(0);
   	
   	mColorBuffer = makeFloatBuffer(colors);
       }
   
       public void draw(GL10 gl) {
   	gl.glVertexPointer(3, GL11.GL_FLOAT, 0, mFVertexBuffer);
   	gl.glColorPointer(4, GL11.GL_FLOAT, 0, mColorBuffer);
   	gl.glDrawElements(GL11.GL_TRIANGLES, 3, GL11.GL_UNSIGNED_BYTE, mIndexBuffer);
       }
   
       private static FloatBuffer makeFloatBuffer(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;
       }
   }
   

   in this class at the row 26 I add the variable colors that contains the information about colors to be assigned in correspondence of the 3 vertices;
   in the draw method at the row 43 I link the colors stored in the buffer mColorBuffer to the vertices of the triangle

3. run the app
   

References:
GLSurfaceView.Renderer
OpenGL ES 1.1 Reference Pages