Channels

Channels are how a shader pass reads anything outside its own code: images, video, audio, other buffers, cubemaps, or keyboard state. In GLSL, those inputs appear as uniforms such as iChannel0, iChannel1, and so on.

Each pass has its own channel grid with up to 16 slots, from iChannel0 to iChannel15. The Image pass, arbitrary named fragment buffer passes, vertex hooks, and Slang compute passes can each access their pass's channels. That means iChannel0 in Image can point to a pass named Flow, while iChannel0 in Flow can point to a noise texture.

Vertex hooks share the pass's channel configuration with mainImage; they do not have a separate channel grid. Sample a configured channel with the generated helper, such as sampleIChannel0(uv). Vertex sampling uses mip level 0. Slang and GLSL vertex files both define mainVertex, with float3/float2 and vec3/vec2 parameters respectively.

What Channels Can Do

Channels are useful in a few different ways:

• Add source media, such as images, videos, audio files, and cubemaps.
• Connect passes together by reading the output of a buffer.
• Build feedback effects by letting a buffer read its own previous frame.
• Make shaders interactive by sampling keyboard state.
• Use per-input metadata such as resolution and playback time.

Adding a Channel

Open the pass you want to configure, then use the channel grid:

1. Click + on an empty slot to add an input.
2. Choose what the channel should read: texture, video, audio, cubemap, buffer, or keyboard.
3. Set the file, source pass, or options for that input.
4. Sample it in GLSL with the matching channel name.

Click an existing channel to edit or remove it. Channels can also be renamed, as long as the name is a valid GLSL identifier.

Note

Shader Studio injects channel uniforms automatically. For most channel types, you do not need to declare uniform sampler2D iChannelN; in your shader.

Sampling Channels in GLSL

The channel slot tells you which uniform to sample. If you add a texture to iChannel0, sample iChannel0. If you add keyboard state to iChannel1, sample iChannel1.

vec2 uv = fragCoord / iResolution.xy;
vec4 inputColor = texture(iChannel0, uv);

Use iChannelResolution[N].xy when the input has a different size than the canvas:

vec2 inputUV = fragCoord / iChannelResolution[0].xy;
vec4 inputColor = texture(iChannel0, inputUV);

Choosing a Channel Type

Use a channel type based on what the shader needs to sample:

Type	Use it for	GLSL sampler
Texture	Static images, noise maps, lookup tables, masks	sampler2D
Video	Moving footage sampled like an image	sampler2D
Audio	FFT and waveform data from an audio file	sampler2D
Cubemap	Skyboxes and environment maps	samplerCube sampled with a vec3 direction
Buffer	Output from another pass, including feedback	sampler2D
Keyboard	Pressed, held, and toggled key state	sampler2D

Every channel also gets metadata uniforms such as iChannelResolution[N], and time-based inputs update iChannelTime[N].

Texture Channels

Bind a static image file to a channel.

Supported formats: png jpg jpeg gif bmp webp tga hdr exr

Option	Values	Default	Description
filter	mipmap / linear / nearest	mipmap	Texture filtering quality
wrap	repeat / clamp	clamp	Edge sampling behaviour
vflip	bool	false	Flip the image vertically
grayscale	bool	false	Convert to luminance (single channel)

vec4 col = texture(iChannel0, uv * 4.0);  // tiling works because wrap = repeat

Tip

Use filter: nearest and wrap: repeat for data textures or pixel-art where blending between texels is undesirable.

Video Channels

Bind a video file. Sampled identically to a texture in GLSL.

Common formats: mp4 webm ogg mov

The container extension alone does not guarantee playback. The video and audio codecs inside the container must also be supported by the browser engine used by your Shader Studio host. Codec availability can differ between a normal browser, VS Code, Electron, and operating systems.

The channel editor includes playback controls — play, pause, next, mute, reset, and a time display. Playback is synced to the shader's play/pause state. The mute button persists to the config as muted: true/false (default false), so a channel's mute state survives reloads and resets.

Note

Pausing the shader pauses the video.

Audio Channels

Bind an audio file. The channel provides a 512×2 texture containing frequency and waveform data each frame.

Common formats: mp3 wav ogg flac aac m4a — plus video containers (mp4 webm mov) that contain an audio stream. Actual codec support depends on the browser engine used by the host; a recognized extension does not guarantee that its encoded audio can be decoded.

If a media file fails to load or its audio plays silently, convert it to a format supported by your target browser or VS Code build. For example, FFmpeg can create an MP3-audio copy of an MP4 while leaving its video stream unchanged:

ffmpeg -i input.mp4 -c:v copy -c:a libmp3lame -q:a 2 output.mp4

Seamless audio loops

MP3, AAC, and other compressed formats can add encoder delay, padding, or a startup transient. These artifacts may cause a click or short gap when an audio channel loops. For the most predictable, sample-continuous audio-channel loops, use uncompressed PCM WAV:

ffmpeg -i input.mp4 -vn -c:a pcm_s16le -ar 48000 output.wav

Texture layout:

Row	y coordinate	Contents
Row 0	≈ 0.25	FFT frequency spectrum — x goes from low to high frequency, value is amplitude 0–1
Row 1	≈ 0.75	Time-domain waveform — x is sample position across the current audio frame

float bass   = texture(iChannel0, vec2(0.05, 0.25)).r; // (1)
float treble = texture(iChannel0, vec2(0.85, 0.25)).r; // (2)
float wave   = texture(iChannel0, vec2(uv.x, 0.75)).r; // (3)

1. Low-frequency FFT bin (x ≈ 0 = bass)
2. High-frequency FFT bin (x ≈ 1 = treble)
3. Waveform value at the current screen column

The channel editor includes a waveform visualiser with draggable handles to set a loop region (startTime / endTime in seconds) and standard playback controls. As with video channels, the mute button persists to the config as muted: true/false (default false).

Tip

The FFT texture layout matches Shadertoy's audio format exactly — audio-reactive shaders from Shadertoy port directly.

Cubemap Channels

Bind a cubemap image for environment mapping or skyboxes. The image must be in cross layout (T-cross PNG), which is the same format Shadertoy uses.

For free cubemap textures, see Humus 3D.

Supported formats: png jpg jpeg hdr exr

Option	Values	Default
filter	mipmap / linear / nearest	mipmap
wrap	clamp / repeat	clamp
vflip	bool	false

Unlike other channel types, a cubemap channel is bound as samplerCube — you must sample it with a 3D direction vector.

vec3 dir = normalize(reflect(rayDir, normal));
vec4 sky  = texture(iChannel0, dir);  // samplerCube lookup — direction, not UV

Warning

Cubemap channels are samplerCube, not sampler2D. Passing a vec2 UV will cause a compile error.

Pass Output (Buffer) Channels

Read the texture output of a renderable pass. The source field accepts arbitrary fragment buffer pass names such as Flow and arbitrary names of Slang compute passes declared with "type": "compute". Referencing a compute pass causes Shader Studio to allocate its output texture. common is shared code rather than a renderable source, and Image cannot be used as a source. Pass names and counts are not limited to BufferA through BufferD.

For a compute pass with outputLayers greater than 1, set layer to select one texture-array layer. It defaults to 0 and must be less than the source pass's outputLayers:

"iChannel0": {
  "type": "buffer",
  "source": "ComputeBlur",
  "layer": 1
}

vec2 bufferUV = fragCoord / iChannelResolution[0].xy;  // use buffer's own resolution
vec4 prev = texture(iChannel0, bufferUV);

Note

Use iChannelResolution[N].xy to get the buffer's resolution for UV mapping, especially if the buffer has a fixed resolution different from the canvas.

Frame timing: a pass samples the current-frame output of a source that runs earlier in the frame. A self-reference or reference to a source that runs later reads that source's previous output. This enables feedback loops, particle trails, and simulations. Compute passes run before fragment buffer passes, then Image runs last.

Keyboard Channels

Bind keyboard state as a texture. No path or options — just add it to a channel slot.

The channel provides a 256×3 texture. Each column is a key code (matching browser e.keyCode values, the same as Shadertoy).

Row	y coordinate	Contents
Row 0	≈ 0.16	Key currently held (255 = held, 0 = not held)
Row 1	≈ 0.50	Key was just pressed this frame
Row 2	≈ 0.83	Toggle — alternates each press

// iChannel1 = keyboard
float held    = texture(iChannel1, vec2(32.0 / 256.0, 0.16)).r;  // Space held
float pressed = texture(iChannel1, vec2(32.0 / 256.0, 0.50)).r;  // Space just pressed

Next

Time and Playback Controls — scrub, loop, and control playback speed