frag

A simple 2D fragment shader viewer, inspired by Shadertoy (www.shadertoy.com)

This tool was designed to support one small feature over and above Shadertoy: the ability to navigate a virtual 2D plane interactively, using the mouse. (This is possible with Shadertoy as well, but it's inconvenient.) I used it to explore a number of algorithms for drawing repeating patterns implicitly (i.e., draw a tiling by sampling positions in the plane rather than pushing polygons through the graphics pipeline).

Launching:

Straightforward, just run a fragment shader:

./frag something.frag

Run a fragment shader that reads from a texture:

./frag -tex some_texture.png something_with_texture.frag

Run a fragment shader that writes in multiple passes to an FBO and then reads from the FBO to write to the screen.

./frag fbo_1.frag fbo_2.frag ... fbo_n.frag compose.frag

The shader:

The program wraps your shader code inside boilerplate containing a few additional declarations via uniforms. The main ones are simple:

• wpos: a vec2d with the 2D world coordinates of the point to sample
• col: a vec4 to hold the output colour.

Your shader should be a function called main() that consumes no arguments and writes to col.

The only other things defined are:

• tex: if an FBO is used, it'll be here.
• tiletex: if a texture is loaded via the commandline, it will be available in a sampler called tiletex.
• resolution: an ivec2D telling you the width and height of the framebuffer.

The program depends on GLFW, STB_IMAGE, and GLM. It's not particularly well written, but it could easily be cleaned up and extended.