BlitPass example

You can find the example project here.

This example shows how to use BlitPass render pass to perform copy between render buffers with the Ramses Composer.

In OpenGL, blitting is an efficient operation to copy rectangular regions between FBOs (represented in Ramses Composer by RenderTargets). It allows to re-use already rendered buffers containing color, depth or other data format in subsequent render passes.

Similarly to the offscreen rendering example, this example first renders the front view of a duck to an offscreen render target. Then it blits color render buffer region to another render buffer four times to create a tiled image. Finally, it uses both render buffers contents to render textured quads, as well as original mesh (seen from default camera), to the default framebuffer.

Scene graph and resources

First, the scene is set up. It contains:

  • Two meshes: a duck and a quad

  • MeshNodes: DuckMeshNode, QuadMeshNodeLeft and QuadMeshNodeRight

  • Two cameras: a DuckCamera for offscreen rendering of the duck front view, and the default PerspectiveCamera for the final scene

All meshes are rendered using TextureMaterial. Note that each MeshNode has a Private Material defined to specify individual texture and toggle UV-flipping. Quad meshes exported from Blender and to flip the V coordinate. The image below cycles through all three Private Materials:

Offscreen rendering

Second, offscreen rendering using DuckRenderPass to DuckRenderBuffer is set up:

  • DuckRenderBuffer using RGBA8 color format and DuckDepthRenderBuffer using Depth24 format are created. They are set to DuckRenderTarget. Binding the depth buffer to the render target allows for depth-test.

  • DuckRenderLayer is created with Renderable Tags set to duck, the tag assigned also to DuckMeshNode mesh.

  • DuckRenderPass is created, specifying rendering of the DuckRenderLayer nodes using DuckCamera to DuckRenderTarget.

  • RenderOrder property of DuckRenderPass is set to 0: it draws to DuckRenderTarget buffers before MainRenderPass reads DuckRenderBuffer as texture for quads. Clear Color property is set to some sort of green.


Next, four BlitPass instances are created. Each one blits the same pixel region with duck’s head from DuckRenderBuffer to BlitRenderBuffer four times in different locations to create a tiled pattern.

  • BlitRenderBuffer is created for blit destination. Its dimensions must match source dimensions.

  • BlitPass with DuckRenderBuffer as Source Render Buffer and BlitRenderBuffer as Target Render Buffer is created.

  • Note that source and destination render buffers must have same dimensions and format. They must be different render buffers.

  • Buffer Offset and Blitting Region dimensions specify the rectangular area to blit.

  • BlitPass RenderOrder is set to 1: it must be executed after DuckRenderPass.

After creating and setting up the first BlitPass, Duplicate (Ctrl+D) command can be used to create three more copies. Blit regions are then specified individually.

Note that all BlitPasses have same RenderOrder. Ramses Composer informs user that their execution order is undefined (as seen on screenshot). In this example, the execution order among BlitPasses does not matter: there is no mutual dependency between them.

Displaying offscreen buffers contents

Finally, to visualize contents of both blit source, DuckRenderBuffer and destination, BlitRenderBuffer, they are set as texture uniforms u_Tex in the Private Material of left and right QuadMeshNodes. Note that u_FlipUV attribute is set to 1, because the Quad mesh has V coordinate flipped.

MainRenderLayer Renderable Tags are set to render_main (for rendering quads) and duck to display original duck mesh side view rendered with default PerspectiveCamera.

MainRenderPass Render Order is set to 3: it is must be executed last, after DuckRenderPass and all BlitPasses, because it depends on their output render buffers.