computer science

Multiple Render Targets

Multiple Render Targets is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Multiple Render Targets rather than just read about it. In short: 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.

Key takeaways

Multiple Render Targets belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Multiple Render Targets to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Multiple Render Targets from memory before moving on to harder problems.

Reference excerpt

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. In deferred shading, this set of textures is commonly called a geometry buffer, or G-buffer. These 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. However, deferred-shading pipelines that rely on MRT can require large G-buffers and significant memory bandwidth, particularly when combined with multisample anti-aliasing (MSAA).

See also Deferred Shading, a shading process that relies heavily on MRT to perform in real-time

References

Worked examples

Example 1 — a first encounter with Multiple Render Targets

Start with the simplest possible case. Write down what Multiple Render Targets claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Multiple Render Targets before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Multiple Render Targets ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Multiple Render Targets

In research: Multiple Render Targets appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Multiple Render Targets in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Multiple Render Targets is common in secondary-school and first-year university syllabi. It links to neighbouring topics 3D rendering, Computer graphics stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Multiple Render Targets outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Multiple Render Targets in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Multiple Render Targets means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Multiple Render Targets out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Multiple Render Targets in simple terms?

Why does Multiple Render Targets matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Multiple Render Targets?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Multiple Render Targets.