Dali - a rendering library for fast digital painting

Dali is a GPU rendering library that creates high quality digital paintings.

Dali is designed to generate output for large canvas prints, which means high DPI, high resolution output. Currently, high resolution images (8000x8000) render in ~20 seconds, plus 40-60 seconds for JPEG encoding.

Getting Started

You can run the example with: cargo run --release --example example

How it works...

Canvas

The canvas is a target image, which is rendered upon by many layers.
Each layer binds a colormap, which is then rendered against with a stipple texture.

Colormaps

Colormaps are target images that each stipple uses for color sampling. Your output image will look like the colormap.

Stipples

Stipples produce texture. Stipples combine their greyscale alpha mask, an optional texture, and the colormap to render the output image. Multiple reference frames and scaling factors are involved, though.

Stipple textures can be:

• translated,
• scaled
• rotated about their center
• (texture) rotated about their center
• deformed by scaling the colormap about the stipple center

Stipples use the colormap to sample color. This sampling occurs in canvas coordinates, which is a different reference frame than the stipple texture! Critically, colormap sampling can be scaled with reference to the center of the stipple in canvas coordinates. This allows a continuous deformation of the colormap image - from 1.0 as a straight copy to 0.0 as a single color.

Stipple textures are optional, but dynamically add contrast to the output. The algorithm is complicated, and described in stipple-texture-fs.glsl.

Intricate textures are generated from many interleaved stipples, each rendering a scaled down version of the colormap.

Intricate colors can be generated by interleaving layers.

All the details

Rendering

Dali uses luminance-rs as a graphics backend.

Dali renders using an OpenGL context, using a fragment shader that covers the stipple's translated coordinates (see and stipple-fs.glsl). See stipple-vs.glsl for all the geometric calculations, and stipple-fs.glsl for the color calculations.

Dali uses OpenGL blending, with premultiplied alpha for better blending quality. I've found that premultiplied alpha blending is good enough to avoid the need to sample from the target buffer and blend in the fragment shader.

Dali uses as much interpolation during sampling as OpenGL will give it, so very high resolution images will be smooth.

When rendering is finished, Dali flattens the premultiplied alpha by setting alpha to 1. This allows visual consistency between GLFW Preview, PNG, and JPEG output. This also avoids the 'divide by zero' problem that premultiplied alpha has.

License

Dali is licensed under Apache 2.0.

Status

Dali is in active development, but is not yet not yet 1.0. Minor changes may be made to the fragment shader.