textmode.js

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Shaders ​

Custom shaders let you generate or process cell data on the GPU. textmode.js uses WebGL2 and expects GLSL ES 3.00 for custom fragment shaders.

Use shaders when a visual is easier to express procedurally or when a CPU loop would be too slow. (｡◕‿◕｡)

Filter shaders ​

createFilterShader() creates a shader from fragment source or a file path:

js
let waveShader;

t.setup(async () => {
  waveShader = await t.createFilterShader("./wave.frag");
});

t.draw(() => {
  t.shader(waveShader);
  t.setUniform("u_time", t.secs);
  t.rect(t.grid.cols, t.grid.rows);
  t.shader(null);
});

shader() sets the current shader. Pass null or call resetShader() to return to the default drawing pipeline.

Uniforms ​

Set one uniform with setUniform():

js
t.setUniform("u_time", t.secs);

Set multiple uniforms with setUniforms():

js
t.setUniforms({
  u_time: t.secs,
  u_center: [0.5, 0.5],
});

MRT outputs ​

Custom filter shaders write three render targets:

glsl
#version 300 es
precision highp float;

in vec2 v_uv;

uniform float u_time;

layout(location = 0) out vec4 o_character;
layout(location = 1) out vec4 o_primaryColor;
layout(location = 2) out vec4 o_secondaryColor;

void main() {
  float wave = sin(v_uv.x * 12.0 + u_time) * 0.5 + 0.5;

  o_character = vec4(wave, 0.0, 0.0, 0.0);
  o_primaryColor = vec4(wave, 1.0 - wave, 1.0, 1.0);
  o_secondaryColor = vec4(0.0, 0.0, 0.0, 1.0);
}

o_character stores glyph selection, transform flags, and character rotation. o_primaryColor stores the glyph color. o_secondaryColor stores the cell color.

Character attachment packing ​

The o_character attachment uses these channels:

  • red: lower 8 bits of the glyph index
  • green: upper 8 bits of the glyph index
  • blue: transform flags
  • alpha: character rotation, where 0.0 to 1.0 maps to 0 to 360 degrees
glsl
int glyph = 65;
float low = float(glyph % 256) / 255.0;
float high = float(glyph / 256) / 255.0;

o_character = vec4(low, high, 0.0, 0.0);

Transform flags are packed into the blue channel:

  • bit 0: invert colors
  • bit 1: flip X
  • bit 2: flip Y
glsl
int invertFlag = 1;
int flipXFlag = 0;
int flipYFlag = 1;

o_character.b = float(invertFlag | (flipXFlag << 1) | (flipYFlag << 2)) / 255.0;

Full shader example ​

Framebuffers and shaders ​

Framebuffers are the usual way to build multi-pass shader pipelines:

js
fb.begin();
t.shader(noiseShader);
t.setUniform("u_time", t.secs);
t.rect(t.grid.cols, t.grid.rows);
t.shader(null);
fb.end();

t.image(fb);

See Framebuffers for offscreen rendering patterns.