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About Ilias Tsagklis

Ilias Tsagklis
Ilias is a software developer turned online entrepreneur. He is co-founder and Executive Editor at Java Code Geeks.

OpenGL ES Texture Mapping

With this example we are going to demonstrate how to perform OpenGL ES Texture mapping (OpenGL ES on Android). We shall create a square and we will apply a texture onto it.

A texture is nothing more than a bitmap image. This method is very useful when creating 2D games and is the preferred way to display images using OpenGL.

In short, to use OpenGL ES Texture Mapping, follow these steps:

  • Create a class (here named Square) responsible for drawing with OpenGL
  • Implement the Android Renderer interface
  • Draw the objects in the onDrawFrame and onSurfaceChanged methods
  • Create an Android activity (here named Run)
  • Use the Android GLSurfaceView to draw the various objects on it

Follow the code snippet(s) below.

package net.obviam.opengl;

import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;

import android.content.Context;
import android.opengl.GLU;
import android.opengl.GLSurfaceView.Renderer;

public class GlRenderer implements Renderer {

	private Square 		square;		// the square
	private Context 	context;

	/** Constructor to set the handed over context */
	public GlRenderer(Context context) {
		this.context = context;

		// initialise the square
		this.square = new Square();
	}

	@Override
	public void onDrawFrame(GL10 gl) {
		// clear Screen and Depth Buffer
		gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);

		// Reset the Modelview Matrix
		gl.glLoadIdentity();

		// Drawing
		gl.glTranslatef(0.0f, 0.0f, -5.0f);		// move 5 units INTO the screen
												// is the same as moving the camera 5 units away
//		gl.glScalef(0.5f, 0.5f, 0.5f);			// scale the square to 50% 
												// otherwise it will be too large
		square.draw(gl);						// Draw the triangle

	}

	@Override
	public void onSurfaceChanged(GL10 gl, int width, int height) {
		if(height == 0) { 						//Prevent A Divide By Zero By
			height = 1; 						//Making Height Equal One
		}

		gl.glViewport(0, 0, width, height); 	//Reset The Current Viewport
		gl.glMatrixMode(GL10.GL_PROJECTION); 	//Select The Projection Matrix
		gl.glLoadIdentity(); 					//Reset The Projection Matrix

		//Calculate The Aspect Ratio Of The Window
		GLU.gluPerspective(gl, 45.0f, (float)width / (float)height, 0.1f, 100.0f);

		gl.glMatrixMode(GL10.GL_MODELVIEW); 	//Select The Modelview Matrix
		gl.glLoadIdentity(); 					//Reset The Modelview Matrix
	}

	@Override
	public void onSurfaceCreated(GL10 gl, EGLConfig config) {
		// Load the texture for the square
		square.loadGLTexture(gl, this.context);

		gl.glEnable(GL10.GL_TEXTURE_2D);			//Enable Texture Mapping ( NEW )
		gl.glShadeModel(GL10.GL_SMOOTH); 			//Enable Smooth Shading
		gl.glClearColor(0.0f, 0.0f, 0.0f, 0.5f); 	//Black Background
		gl.glClearDepthf(1.0f); 					//Depth Buffer Setup
		gl.glEnable(GL10.GL_DEPTH_TEST); 			//Enables Depth Testing
		gl.glDepthFunc(GL10.GL_LEQUAL); 			//The Type Of Depth Testing To Do

		//Really Nice Perspective Calculations
		gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT, GL10.GL_NICEST); 

	}

}
package net.obviam.opengl;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;

import javax.microedition.khronos.opengles.GL10;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.opengl.GLUtils;

public class Square {

	private FloatBuffer vertexBuffer;	// buffer holding the vertices
	private float vertices[] = {
			-1.0f, -1.0f,  0.0f,		// V1 - bottom left
			-1.0f,  1.0f,  0.0f,		// V2 - top left
			 1.0f, -1.0f,  0.0f,		// V3 - bottom right
			 1.0f,  1.0f,  0.0f			// V4 - top right
	};

	private FloatBuffer textureBuffer;	// buffer holding the texture coordinates
	private float texture[] = {    		
			// Mapping coordinates for the vertices
			0.0f, 1.0f,		// top left		(V2)
			0.0f, 0.0f,		// bottom left	(V1)
			1.0f, 1.0f,		// top right	(V4)
			1.0f, 0.0f		// bottom right	(V3)
	};

	/** The texture pointer */
	private int[] textures = new int[1];

	public Square() {
		// a float has 4 bytes so we allocate for each coordinate 4 bytes
		ByteBuffer byteBuffer = ByteBuffer.allocateDirect(vertices.length * 4);
		byteBuffer.order(ByteOrder.nativeOrder());

		// allocates the memory from the byte buffer
		vertexBuffer = byteBuffer.asFloatBuffer();

		// fill the vertexBuffer with the vertices
		vertexBuffer.put(vertices);

		// set the cursor position to the beginning of the buffer
		vertexBuffer.position(0);

		byteBuffer = ByteBuffer.allocateDirect(texture.length * 4);
		byteBuffer.order(ByteOrder.nativeOrder());
		textureBuffer = byteBuffer.asFloatBuffer();
		textureBuffer.put(texture);
		textureBuffer.position(0);
	}

	/**
	 * Load the texture for the square
	 * @param gl
	 * @param context
	 */
	public void loadGLTexture(GL10 gl, Context context) {
		// loading texture
		Bitmap bitmap = BitmapFactory.decodeResource(context.getResources(),
				R.drawable.android);

		// generate one texture pointer
		gl.glGenTextures(1, textures, 0);
		// ...and bind it to our array
		gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[0]);

		// create nearest filtered texture
		gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MIN_FILTER, GL10.GL_NEAREST);
		gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR);

		//Different possible texture parameters, e.g. GL10.GL_CLAMP_TO_EDGE
//		gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_S, GL10.GL_REPEAT);
//		gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_T, GL10.GL_REPEAT);

		// Use Android GLUtils to specify a two-dimensional texture image from our bitmap 
		GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, bitmap, 0);

		// Clean up
		bitmap.recycle();
	}

	/** The draw method for the square with the GL context */
	public void draw(GL10 gl) {
		// bind the previously generated texture
		gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[0]);

		// Point to our buffers
		gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
		gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);

		// Set the face rotation
		gl.glFrontFace(GL10.GL_CW);

		// Point to our vertex buffer
		gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer);
		gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, textureBuffer);

		// Draw the vertices as triangle strip
		gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, vertices.length / 3);

		//Disable the client state before leaving
		gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
		gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
	}
}
package net.obviam.opengl;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;

import javax.microedition.khronos.opengles.GL10;

public class Triangle {

	private FloatBuffer vertexBuffer;	// buffer holding the vertices

	private float vertices[] = {
			-0.5f, -0.5f,  0.0f,		// V1 - first vertex (x,y,z)
			 0.5f, -0.5f,  0.0f,		// V2 - second vertex
			 0.0f,  0.5f,  0.0f			// V3 - third vertex
//			 1.0f,  0.5f,  0.0f			// V3 - third vertex
	};

	public Triangle() {
		// a float has 4 bytes so we allocate for each coordinate 4 bytes
		ByteBuffer vertexByteBuffer = ByteBuffer.allocateDirect(vertices.length * 4);
		vertexByteBuffer.order(ByteOrder.nativeOrder());

		// allocates the memory from the byte buffer
		vertexBuffer = vertexByteBuffer.asFloatBuffer();

		// fill the vertexBuffer with the vertices
		vertexBuffer.put(vertices);

		// set the cursor position to the beginning of the buffer
		vertexBuffer.position(0);

	}

	/** The draw method for the triangle with the GL context */
	public void draw(GL10 gl) {

		gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
		// set the colour for the background
//		gl.glClearColor(0.0f, 0.0f, 0.0f, 0.5f);

		// to show the color (paint the screen) we need to clear the color buffer
//		gl.glClear(GL10.GL_COLOR_BUFFER_BIT);

		// set the colour for the triangle
		gl.glColor4f(0.0f, 1.0f, 0.0f, 0.5f);

		// Point to our vertex buffer
		gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer);

		// Draw the vertices as triangle strip
		gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, vertices.length / 3);

		//Disable the client state before leaving
		gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
	}
}
package net.obviam.opengl;

import android.app.Activity;
import android.opengl.GLSurfaceView;
import android.os.Bundle;
import android.view.Window;
import android.view.WindowManager;

public class Run extends Activity {

	/** The OpenGL view */
	private GLSurfaceView glSurfaceView;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {

  super.onCreate(savedInstanceState);

  // requesting to turn the title OFF

  requestWindowFeature(Window.FEATURE_NO_TITLE);

  // making it full screen
		getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
				WindowManager.LayoutParams.FLAG_FULLSCREEN);

  // Initiate the Open GL view and

  // create an instance with this activity

  glSurfaceView = new GLSurfaceView(this);

  // set our renderer to be the main renderer with

  // the current activity context

  glSurfaceView.setRenderer(new GlRenderer(this));

  setContentView(glSurfaceView);
    }

	/**
	 * Remember to resume the glSurface
	 */
	@Override
	protected void onResume() {
		super.onResume();
		glSurfaceView.onResume();
	}

	/**
	 * Also pause the glSurface
	 */
	@Override
	protected void onPause() {
		super.onPause();
		glSurfaceView.onPause();
	}

}

 
This was an example of how to use OpenGL ES Texture Mapping.

Related Article:

Reference: Texture Mapping – OpenGL Android (Displaying Images using OpenGL and Squares) from our JCG partner Tamas Jano at the “Against The Grain” blog.

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