ShaderLesson2 Ported to LibGDX

ShaderLesson2LibGDX.java

import com.badlogic.gdx.ApplicationListener;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.backends.lwjgl.LwjglApplication;
import com.badlogic.gdx.backends.lwjgl.LwjglApplicationConfiguration;
import com.badlogic.gdx.graphics.GL10;
import com.badlogic.gdx.graphics.OrthographicCamera;
import com.badlogic.gdx.graphics.Texture;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import com.badlogic.gdx.graphics.glutils.ShaderProgram;

/**
 * A port of ShaderLesson2 from lwjgl-basics to LibGDX:
 * https://github.com/mattdesl/lwjgl-basics/wiki/ShaderLesson2
 * 
 * @author davedes
 */
public class ShaderLesson2 implements ApplicationListener {
	
	//Minor differences: 
		//LibGDX Position attribute is a vec4
		//u_projView is called u_projTrans
		//we need to set ShaderProgram.pedantic to false 
		//LibGDX uses lower-left as origin (0, 0)
		//TexCoord attribute requires "0" appended at end to denote GL_TEXTURE0
			//ShaderProgram.TEXCOORD_ATTRIBUTE+"0"
		//It's wise to use LOWP for color attribute in GL ES
	
	public static void main(String[] args) {
		LwjglApplicationConfiguration cfg = new LwjglApplicationConfiguration();
		cfg.title = "Shader Lesson 2";
		cfg.useGL20 = true;
		cfg.width = 640;
		cfg.height = 480;
		cfg.resizable = false;

		new LwjglApplication(new ShaderLesson2(), cfg);
	}
	
	final String VERT =  
			"attribute vec4 "+ShaderProgram.POSITION_ATTRIBUTE+";\n" +
			"attribute vec4 "+ShaderProgram.COLOR_ATTRIBUTE+";\n" +
			"attribute vec2 "+ShaderProgram.TEXCOORD_ATTRIBUTE+"0;\n" +
			
			"uniform mat4 u_projTrans;\n" + 
			" \n" + 
			"varying vec4 vColor;\n" +
			"varying vec2 vTexCoord;\n" +
			
			"void main() {\n" +  
			"	vColor = "+ShaderProgram.COLOR_ATTRIBUTE+";\n" +
			"	vTexCoord = "+ShaderProgram.TEXCOORD_ATTRIBUTE+"0;\n" +
			"	gl_Position =  u_projTrans * " + ShaderProgram.POSITION_ATTRIBUTE + ";\n" +
			"}";
	
	final String FRAG = 
			//GL ES specific stuff
			  "#ifdef GL_ES\n" //
			+ "#define LOWP lowp\n" //
			+ "precision mediump float;\n" //
			+ "#else\n" //
			+ "#define LOWP \n" //
			+ "#endif\n" + //
			"varying LOWP vec4 vColor;\n" +
			"varying vec2 vTexCoord;\n" + 
			"uniform sampler2D u_texture;\n" +			
			"void main() {\n" +  
			"	vec4 texColor = texture2D(u_texture, vTexCoord);\n" + 
			"	\n" + 
			"	texColor.rgb = 1.0 - texColor.rgb;\n" + 
			"	\n" + 
			"	gl_FragColor = texColor * vColor;\n" + 
			"}";
	
	Texture tex;
	SpriteBatch batch;
	OrthographicCamera cam;
	ShaderProgram shader;
	 
	@Override
	public void create() {
		tex = new Texture(Gdx.files.internal("data/grass.png"));
		
		//important since we aren't using some uniforms and attributes that SpriteBatch expects
		ShaderProgram.pedantic = false;

		shader = new ShaderProgram(VERT, FRAG);
		if (!shader.isCompiled()) {
			System.err.println(shader.getLog());
			System.exit(0);
		}
		if (shader.getLog().length()!=0)
			System.out.println(shader.getLog());
		
		
		batch = new SpriteBatch(1000, shader);
		batch.setShader(shader);
		
		cam = new OrthographicCamera(Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
		cam.setToOrtho(false);
	}

	@Override
	public void resize(int width, int height) {
		cam.setToOrtho(false, width, height);
		batch.setProjectionMatrix(cam.combined);
	}

	@Override
	public void render() {
		Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
		
		batch.begin();
		
		//notice that LibGDX coordinate system origin is lower-left
		batch.draw(tex, 10, 10);
		batch.draw(tex, 10, 320, 32, 32);
		
		batch.end();
	}

	@Override
	public void pause() {
		
	}

	@Override
	public void resume() {
		
	}

	@Override
	public void dispose() {
		batch.dispose();
		shader.dispose();
		tex.dispose();
	}	
}