OffscreenRenderHelper Class Reference

#include <ImFusion/Core/GL/OffscreenRenderHelper.h>

Helper class to perform deferred off-screen rendering. More...

Inheritance diagram for OffscreenRenderHelper:

Detailed Description

Helper class to perform deferred off-screen rendering.

This class helps you to accumulate your rendering calls into a temporary texture before eventually copying/blending the accumulated pixels back to the original/parent framebuffer. Internally, the temporary textures and framebuffer objects are cached and reused if compatible to avoid performance issues due to constant reallocation.

A typical usage scenario looks like this:

// setup custom FBO and attach temporary texture to render into
auto renderBuffer = GL::OffscreenRenderHelper::cachedInstance().create(viewportSize);
 
// render scene
renderX();
renderY();
...
 
// stop using the temporary FBO and copy/blend its contents back to the original framebuffer
renderBuffer.blendToParent();

Note

This interface is still experimental and its API may change significantly in the future.

Classes
struct	RenderBuffer
	Helper structure to encapsulate OpenGL objects representing the temporary rendering buffer. More...

Public Types
enum class	ColorPostProcessing { None = 0 , DivideByAlpha = 1 , DivideBySqrtAlpha = 2 }
	Enumeration of optional additional color processing steps to perform in the copy shader. More...

Public Member Functions
RenderBuffer	create (const vec2i &viewportSize, GL::InternalFormat colorFormat=GL::InternalFormat::RGBA8, GL::InternalFormat depthFormat=GL::InternalFormat::DepthComponent24)
	Creates a new temporary render buffer of the given configuration for off-screen rendering.
int	cacheSize () const
	Returns the maximum number of RenderBuffer instances that are cached by OffscreenRenderHelper.
void	setCacheSize (int numElements)
	Sets the maximum number of RenderBuffer instances that are cached by OffscreenRenderHelper; must not be negative.

Additional Inherited Members
Static Public Member Functions inherited from InstanceManager< OffscreenRenderHelper >
static OffscreenRenderHelper &	cachedInstance ()
	Returns the cached instance of type T for the currently active OpenGL context.

Member Enumeration Documentation

ColorPostProcessing

enum class ColorPostProcessing

strong

Enumeration of optional additional color processing steps to perform in the copy shader.

Enumerator
None	Write the original RGBA value of the color texture to the fragment shader output.
DivideByAlpha	Divide the RGB value by the alpha component. This is useful if you are using pre-multiplied alpha blending and want to reverse the pre-multiplication process in a single pass.
DivideBySqrtAlpha	Divide the RGBA value by sqrt(A). If your blending setup is (SrcAlpha, OneMinusSourceAlpha) this option allows for the final result after blendToParentAndDispose() being the same as if you would directly render to the parent framebuffer without usage of OffscreenRenderHelper.

Member Function Documentation

create()

RenderBuffer create ( const vec2i & viewportSize, GL::InternalFormat colorFormat = GL::InternalFormat::RGBA8, GL::InternalFormat depthFormat = GL::InternalFormat::DepthComponent24 )

nodiscard

Creates a new temporary render buffer of the given configuration for off-screen rendering.

After calling this function and capturing the returned RenderBuffer the current OpenGL context will have bound a dedicated FBO with one color and one depth texture of the given formats attached. The textures will be cleared with color vec4(0, 0, 0, 0) and depth 1 and the OpenGL viewport will be set to size viewportSize with offset (0, 0).

The original FBO and viewport state will be restored when the RenderBuffer is destroyed or you call RenderBuffer::blendToParent().

Parameters

viewportSize	Size in pixels of the temporary render buffer
colorFormat	Internal texture format to use for the color attachment.
depthFormat	Internal texture format to use for the depth attachment.

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The documentation for this class was generated from the following file:

• ImFusion/Core/GL/OffscreenRenderHelper.h