Multiple Render Targets
Encyclopedia
In the field of 3D computer graphics
, Multiple Render Targets, or MRT, is a feature of modern graphics processing units (GPUs) that allows the programmable rendering pipeline to render images to multiple render target textures
at once. These textures can then be used as inputs to other shaders or as texture maps applied to 3D models. Introduced by OpenGL
2.0 and Direct3D
9, MRT can be invaluable to real-time 3D applications such as video games. Before the advent of MRT, a programmer would have to issue a command to the GPU to draw the 3D scene once for each render target texture, resulting in redundant vertex transformations which, in a real-time program expected to run as fast as possible, can be quite time-consuming. With MRT, a programmer creates a pixel shader that returns an output value for each render target. This pixel shader then renders to all render targets with a single draw command.
A common use of MRT is deferred shading
, a shading process which, unlike forward shading, performs lighting calculations on an entire 3D scene at once instead of on each individual object. To do this in real-time, MRT is used to store the required information for the lighting calculations in multiple render targets, which are then used after the entire scene has been drawn to calculate the lit final image. Typically one render target holds color and surface information of objects, while another contains the surface normals and depth information of the scene which are used to calculate the reflection of light. Additional render targets can be used to store information such as the specularity
of the surface and ambient occlusion
data.
3D computer graphics
3D computer graphics are graphics that use a three-dimensional representation of geometric data that is stored in the computer for the purposes of performing calculations and rendering 2D images...
, Multiple Render Targets, or MRT, is a feature of modern graphics processing units (GPUs) that allows the programmable rendering pipeline to render images to multiple render target textures
Render Target
In the field of 3D computer graphics, a render target is a feature of modern graphics processing units that allows a 3D scene to be rendered to an intermediate memory buffer, or Render Target Texture , instead of the frame buffer or back buffer...
at once. These textures can then be used as inputs to other shaders or as texture maps applied to 3D models. Introduced by OpenGL
OpenGL
OpenGL is a standard specification defining a cross-language, cross-platform API for writing applications that produce 2D and 3D computer graphics. The interface consists of over 250 different function calls which can be used to draw complex three-dimensional scenes from simple primitives. OpenGL...
2.0 and Direct3D
Direct3D
Direct3D is part of Microsoft's DirectX application programming interface . Direct3D is available for Microsoft Windows operating systems , and for other platforms through the open source software Wine. It is the base for the graphics API on the Xbox and Xbox 360 console systems...
9, MRT can be invaluable to real-time 3D applications such as video games. Before the advent of MRT, a programmer would have to issue a command to the GPU to draw the 3D scene once for each render target texture, resulting in redundant vertex transformations which, in a real-time program expected to run as fast as possible, can be quite time-consuming. With MRT, a programmer creates a pixel shader that returns an output value for each render target. This pixel shader then renders to all render targets with a single draw command.
A common use of MRT is deferred shading
Deferred shading
In computer graphics, deferred shading is a three dimensional shading technique in which the result of a shading algorithm is calculated by dividing it into smaller parts that are written to intermediate buffer storage to be combined later, instead of immediately writing the shader result to the...
, a shading process which, unlike forward shading, performs lighting calculations on an entire 3D scene at once instead of on each individual object. To do this in real-time, MRT is used to store the required information for the lighting calculations in multiple render targets, which are then used after the entire scene has been drawn to calculate the lit final image. Typically one render target holds color and surface information of objects, while another contains the surface normals and depth information of the scene which are used to calculate the reflection of light. Additional render targets can be used to store information such as the specularity
Specularity
Specularity is the visual appearance of specular reflections. In computer graphics, it meansthe quantity used in 3D rendering which represents the amount of specular reflectivity a surface has...
of the surface and ambient occlusion
Ambient occlusion
Ambient occlusion is a shading method used in 3D computer graphics which helps add realism to local reflection models by taking into account attenuation of light due to occlusion...
data.
See also
- Deferred ShadingDeferred shadingIn computer graphics, deferred shading is a three dimensional shading technique in which the result of a shading algorithm is calculated by dividing it into smaller parts that are written to intermediate buffer storage to be combined later, instead of immediately writing the shader result to the...
, a shading process that relies heavily on MRT to perform in real-time