CODEWITHSUNDEEP
opengllibgdx
Hải Phong
Hải Phong

Reputation: 5144

How to draw on just a portion of the screen with SpriteBatch in libgdx?

When I do this:

SpriteBatch spriteBatch = new SpriteBatch();
spriteBatch.setProjectionMatrix(new Matrix4().setToOrtho(0, 320, 0, 240, -1, 1));
spriteBatch.begin();
spriteBatch.draw(textureRegion, 0, 0);
spriteBatch.end();

SpriteBatch will draw the textureRegion onto the coordinate system 320-240 that I have specified to the whole screen. Say I want to draw with the same coordinate system 320 240 but only on the left half of the screen (which means everything will be scaled down horizontally in the left side, leaving the right half of the screen black), how can I do?

Upvotes: 1

Views: 3149

Answers (4)

Tashus
Tashus

Reputation: 217

Before rendering the batch, you can set the viewport to draw on a specific screen area. The important line is:

Gdx.gl.glViewport(x, y, w, h);

The viewport usually starts at x = 0 and y = 0 and extends to the full width and height of the screen. If we want to see only a part of that original viewport, we need to change both the size and the starting position. To draw only on the left half of the screen, use:

x = 0;
y = 0;
w = Gdx.graphics.getWidth()/2;
h = Gdx.graphics.getWidth();

I found the solution here and originally answered this question to a slightly more complicated problem, but the technique is the same.

To focus on any different portion of the viewport, simply choose x, y, w, and h accordingly. If you're going to do any more rendering in the normal fashion, make sure to reset the viewport with the original x, y, w, and h values.

Upvotes: 1

Mickäel A.
Mickäel A.

Reputation: 9377

You could either

  • double the viewport width of the SpriteBatch
  • use a Sprite and set its width scale to 0.5f (be careful about the origin) and use its draw(SpriteBatch) method to draw it.

Upvotes: 0

R Hyde
R Hyde

Reputation: 10409

Perhaps I am misunderstanding the question, but could you not just double the viewport width, setting it to 640 instead of 320?

SpriteBatch spriteBatch = new SpriteBatch;
spriteBatch.setProjectionMatrix(new Matrix4().setToOrtho(0, 640, 0, 240, -1, 1));
spriteBatch.begin();
spriteBatch.draw(textureRegion, 0, 0);
spriteBatch.end();

Upvotes: 0

Jeremy Scoggins
Jeremy Scoggins

Reputation: 954

You're going to want to use the ScissorStack. Effectively, you define a rectangle that you want to draw in. All drawing will be in the rectangle that you defined. 

Rectangle scissors = new Rectangle(); 
Rectangle clipBounds = new Rectangle(x,y,w,h);
ScissorStack.calculateScissors(camera, spriteBatch.getTransformMatrix(), clipBounds, scissors); 
ScissorStack.pushScissors(scissors); 
spriteBatch.draw(...); 
spriteBatch.flush();    
ScissorStack.popScissors();

This will limit rendering to within the bounds of the rectangle "clipBounds". It is also possible push multiple rectangles. Only the pixels of the sprites that are within all of the rectangles will be rendered.

From http://code.google.com/p/libgdx/wiki/GraphicsScissors

Upvotes: 6

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