SpriteBatch setProjectionMatrix woes...

Engines, Libraries and Tools
#1

I want to render an image at coordinates 100, 50, 0. Consider the following code…


package com.mygdx.game;
import com.badlogic.gdx.ApplicationAdapter;

import scenegraph.*;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.graphics.GL20;
import com.badlogic.gdx.graphics.OrthographicCamera;
import com.badlogic.gdx.graphics.Texture;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import com.badlogic.gdx.graphics.g2d.TextureRegion;
import com.badlogic.gdx.math.Matrix4;


/**
 * Object representing the core of the game.  Which platform it compiles for
 * varies
 * @author William Andrew Cahill
 */
public class GameLauncher extends ApplicationAdapter 
{
	// Rendering variables
	private SpriteBatch batch;			// Object that renders all the sprites
	
	// Region to draw
	TextureRegion region;
	
	
	@Override
	public void create()
	{
		// Initializes batch
		batch = new SpriteBatch();
		
		// Stores first image
		region = new TextureRegion(new Texture(Gdx.files.internal("res/entities/wiggles/wigglesIdle.png")));
	}

	
	@Override
	public void render()
	{
		// Clears the screen
		Gdx.gl.glClearColor(1, 0, 0, 1);
		Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
		
		// Begins drawing
		batch.begin();
		
		// Gets matrix and copy
		Matrix4 m = batch.getProjectionMatrix();
		Matrix4 c = m.cpy();
		
		// Draws
		m.translate(100, 50, 0);
		batch.draw(region,0,0);
		
		// Restores matrix
		batch.setProjectionMatrix(c);
		
		// Ends drawing
		batch.end();
	}
}

No matter what transformations I make, it stays in the same place. I know that there is a draw method in SpriteBatch that lets me specify where to draw it, but I am trying to set up a scene-graph, and that requires me to translate, rotate, etc using SpriteBatch’s Matrix4 extracted from batch.getProjectionMatrix(). I can make it look like the image slides across the screen if I remove the line that restores the matrix to it’s original form, but I can’t make it shift and stay there. Is my understanding of the projection matrix incorrect? I always have this problem with LibGDX, but I can never remember how to solve it. The docs don’t really explain its behavior.

#2

Aaaaand I solve my own problem only after I post something and make myself look like an idiot xD. I should have extracted the matrix and transformed it BEFORE calling begin/end. Like this:


package com.mygdx.game;
import com.badlogic.gdx.ApplicationAdapter;

import scenegraph.*;

import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.graphics.GL20;
import com.badlogic.gdx.graphics.OrthographicCamera;
import com.badlogic.gdx.graphics.Texture;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import com.badlogic.gdx.graphics.g2d.TextureRegion;
import com.badlogic.gdx.math.Matrix4;


/**
 * Object representing the core of the game.  Which platform it compiles for
 * varies
 * @author William Andrew Cahill
 */
public class GameLauncher extends ApplicationAdapter 
{
	// Rendering variables
	private SpriteBatch batch;			// Object that renders all the sprites
	
	// Region to draw
	TextureRegion region;
	
	
	@Override
	public void create()
	{
		// Initializes batch
		batch = new SpriteBatch();
		
		// Stores first image
		region = new TextureRegion(new Texture(Gdx.files.internal("res/entities/wiggles/wigglesIdle.png")));
	}

	
	@Override
	public void render()
	{
		// Clears the screen
		Gdx.gl.glClearColor(1, 0, 0, 1);
		Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
		
		// Begins drawing
		// Gets matrix and copy
		Matrix4 m = batch.getProjectionMatrix();
		Matrix4 c = m.cpy();
		
		// Draws
		m.translate(100, 1, 0);
		batch.begin();
		
		batch.draw(region,0,0);
		
		// Restores matrix
		batch.setProjectionMatrix(c);
		
		// Ends drawing
		batch.end();
	}
}

As you were…