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<p class="license">This tutorial is the Render Techniques chapter from <em><a href="../../handbook">Processing: A Programming Handbook for Visual Designers and Artists, Second Edition</a></em>, published by MIT Press. &copy; 2014 MIT Press. If you see any errors or have comments, please <a href="https://github.com/processing/processing-docs/issues?state=open">let us know</a>.</p>

<h1 style="line-height: 0.7em;">Render Techniques</h1>

<h3 style="line-height: 0.7em;"><em>Casey Reas and Ben Fry</em></h3>

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Throughout this book, everything has drawn to the primary display window. Sometimes, however, there is an advantage in drawing to another graphics surface. All of the drawing features available in the display window can be applied to an offscreen drawing surface and then drawn back into the display window as an image or texture. This technique makes it easier to imagine a program as a stack of layers similar to the technique used in photo editing and vector drawing software. Similarly, drawing surfaces in Processing can be moved around, drawn using blending effects and transparency, and drawn in different orders to change how the layers combine. Before the discussion moves to multiple drawing surfaces, this chapter starts with a discussion of the different renderers used by Processing.

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This short text provides a brief history of the digital printing technologies that have led to these new techniques. It presents examples of software written to produce print output, and discusses a few common contemporary print technologies. The industry surrounding digital printing is full of trademarked names and buzzwords, so this text aspires to demystify some of the terminology and provide pointers to additional information. The content that follows is tailored for printing at home or working with a vendor to produce small editions.

Processing has three primary renderers: the default renderer, P3D, and P2D. The default renderer is used for the majority of the programs in this book; it’s for 2D drawing. It’s used when one of the other renders aren’t defined as the third parameter to size(). The P3D renderer for drawing in three dimensions is discussed in the 3D Drawing chapter (p. 21). The P2D renderer is an alternative 2D renderer that is substantially faster than the default renderer for most tasks, but it sacrifices some visual quality for speed. Both P2D and P3D utilize a software specification called OpenGL that is supported on many GPUs (the Graphics Processing Unit on a computer’s graphics card) to accelerate drawing. The visual quality of the OpenGL renderers, P2D and P3D, can be adjusted with the smooth() and hint() functions.

All programs have smoothing enabled by default, but an optional parameter to smooth() can improve the quality of the OpenGL rendering with P2D and P3D. For instance, smooth(4) will enhance the quality of anti-aliasing to improve the image quality. The optional parameters from low to high are 2, 4, and 8, with 2 as the default. These options are only available on graphics cards that support them and may slow a program down or require more memory.

The hint() function is available for advanced users to modify details about how geometry is drawn to the screen. By default, when rendering a scene, each renderer makes decisions about drawing order, shape occlusion, perspective distortion, and so on based on what is more likely to be useful and efficient for the largest number of users. Hints are used to change these defaults if other decisions are better for a specific program. There is a single hint() function, but the parameters for it enable and disable a range of rendering decisions. For example, to make lines appear in perspective, write hint(ENABLE_STROKE_PERSPECTIVE) and to turn this back off, write hint(DISABLE_STROKE_PERSPECTIVE). This feature is not enabled by default because it’s slower and will make lines in predominantly flat scenes appear strangely. But it’s a useful necessity when drawing many lines that make use of a large 3D space. The parameters to hint() change over time, so please consult the Processing reference for the current options.

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