libgdx-framebuffer-pixmap

libGDX FrameBuffer & Pixmap

Quick reference for render-to-texture (FBO) and CPU-side pixel manipulation. Covers FrameBuffer, GLFrameBuffer, FloatFrameBuffer, Pixmap, PixmapIO, and Color int conversions.

FrameBuffer (FBO)

com.badlogic.gdx.graphics.glutils.FrameBuffer extends GLFrameBuffer<Texture>, implements Disposable.

Construction

// Standard — width/height in PIXELS, not world units
FrameBuffer fbo = new FrameBuffer(Pixmap.Format.RGBA8888, width, height, hasDepth);
FrameBuffer fbo = new FrameBuffer(Pixmap.Format.RGBA8888, width, height, hasDepth, hasStencil);

// Typical: match screen resolution
FrameBuffer fbo = new FrameBuffer(Pixmap.Format.RGBA8888,
    Gdx.graphics.getBackBufferWidth(), Gdx.graphics.getBackBufferHeight(), false);

• hasDepth adds a 16-bit depth renderbuffer (GL_DEPTH_COMPONENT16).
• hasStencil adds an 8-bit stencil renderbuffer (GL_STENCIL_INDEX8).
• Width/height are pixel dimensions. Do NOT pass world units or viewport units.

begin() / end() Pattern

fbo.begin();
// Binds FBO + sets glViewport to FBO dimensions.
// Does NOT save previous framebuffer or viewport state.
ScreenUtils.clear(0, 0, 0, 1);  // MUST clear — previous frame persists otherwise
batch.setProjectionMatrix(camera.combined);
batch.begin();
// ... render scene into FBO ...
batch.end();
fbo.end();
// Unbinds FBO (binds default framebuffer) + restores viewport to back buffer size.

end(int x, int y, int width, int height) — restores a specific viewport instead of auto-detecting back buffer size.

Gotchas:

• begin() does NOT save previous state. end() ALWAYS unbinds to the default framebuffer. There is no stack.
• You MUST clear after begin() — the FBO retains content from the previous frame.
• The camera/projection matrix used inside the FBO should match the FBO's dimensions, not the screen.

Drawing the FBO Texture to Screen

The FBO texture is vertically flipped (OpenGL renders Y-up but textures sample Y-down). You MUST flip it: