ShaderLesson4.java

package atmos.tool2d;

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 ShaderLesson4 from lwjgl-basics to LibGDX:
 * https://github.com/mattdesl/lwjgl-basics/wiki/ShaderLesson4
 * 
 * @author davedes
 */
public class ShaderLesson4 implements ApplicationListener {
  
  //Minor differences: 
		//LibGDX Position attribute is a vec4
		//u_projView is called u_projTrans
		//we need to set ShaderProgram.pedantic to false 
		//TexCoord attribute requires "0" appended at end to denote GL_TEXTURE0
			//ShaderProgram.TEXCOORD_ATTRIBUTE+"0"
		//It's wise to use LOWP when possible in GL ES
		//In LibGDX ShaderProgram uses begin() and end()
		//we can use Texture.bind(int) to bind a texture unit
		//note that it will leave that unit active -- so we need to reset to zero after!
	
	public static void main(String[] args) {
		LwjglApplicationConfiguration cfg = new LwjglApplicationConfiguration();
		cfg.title = "Shader Lesson - LibGDX";
		cfg.useGL20 = true;
		cfg.width = 320;
		cfg.height = 240;
		cfg.resizable = false;

		new LwjglApplication(new ShaderLesson4(), 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" +	
			"uniform sampler2D u_texture1;\n" +
			"uniform sampler2D u_mask;\n" +	
			"void main(void) {\n" + 
			"	//sample the colour from the first texture\n" + 
			"	vec4 texColor0 = texture2D(u_texture, vTexCoord);\n" + 
			"\n" + 
			"	//sample the colour from the second texture\n" + 
			"	vec4 texColor1 = texture2D(u_texture1, vTexCoord);\n" + 
			"\n" + 
			"	//get the mask; we will only use the alpha channel\n" + 
			"	float mask = texture2D(u_mask, vTexCoord).a;\n" + 
			"\n" + 
			"	//interpolate the colours based on the mask\n" + 
			"	gl_FragColor = vColor * mix(texColor0, texColor1, mask);\n" + 
			"}";
	
	Texture tex0, tex1, mask;
	SpriteBatch batch;
	OrthographicCamera cam;
	ShaderProgram shader;
	 
	@Override
	public void create() {
		tex0 = new Texture(Gdx.files.internal("data/grass.png"));
		tex1 = new Texture(Gdx.files.internal("data/dirt.png"));
		mask = new Texture(Gdx.files.internal("data/mask.png"));
		
		//important since we aren't using some uniforms and attributes that SpriteBatch expects
		ShaderProgram.pedantic = false;
		
		//print it out for clarity
		System.out.println("Vertex Shader:\n-------------\n\n"+VERT);
		System.out.println("\n");
		System.out.println("Fragment Shader:\n-------------\n\n"+FRAG);
		
		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());
		

		shader.begin();
		shader.setUniformi("u_texture1", 1);
		shader.setUniformi("u_mask", 2);
		shader.end();
		
		//bind mask to glActiveTexture(GL_TEXTURE2)
		mask.bind(2);
		
		//bind dirt to glActiveTexture(GL_TEXTURE1)
		tex1.bind(1);
		
		//now we need to reset glActiveTexture to zero!!!! since sprite batch does not do this for us
		Gdx.gl.glActiveTexture(GL10.GL_TEXTURE0);
		
		//tex0 will be bound when we call SpriteBatch.draw 
		
		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();
		
		batch.draw(tex0, 0, 0);
		
		batch.end();
	}

	@Override
	public void pause() {
		
	}

	@Override
	public void resume() {
		
	}

	@Override
	public void dispose() {
		batch.dispose();
		shader.dispose();
		tex0.dispose();
	}	
}