Shader Constants, Variables, and Outputs

Below are tables of shader constants and variables that are available to you, provided by Indigo, when writing shaders for the WebGL 2.0 renderer.

To clarify terminology use on this page:

1. "Constants" are fixed values that never change.
2. "Variables" are values that you should treat as read only, and that will change between program runs.
3. "Outputs" are values that you may be able to read, and may wish to write to in order to affect the final rendering.

Common

These values are available to all shader programs.

Constants

Name	Type	Description
PI	float	3.141592653589793 or 180 degrees.
PI_2	float	PI / 2 or 90 degrees.
PI_4	float	PI / 4 or 45 degrees.
TAU	float	2.0 * PI or 360 degrees.
TAU_2	float	PI or 180 degrees.
TAU_4	float	PI / 2 or 90 degrees.
TAU_8	float	PI / 4 or 45 degrees.

Variables (read only)

Name	Type	Description
TIME	float	Running time in seconds.
VIEWPORT_SIZE	vec2	Size of the viewport in pixels.

Vertex Shader Programs

Note that SIZE and UV are treated differently between entity and blend shaders, this may be revised in the future.

Common

Outputs (read/write)

Name	Type	Description
VERTEX	vec4	The output position of the current vertex.

Entity Shader Specific

Variables (read only)

Name	Type	Description
ATLAS_SIZE	vec2	Size of the atlas this texture is on, in pixels.
CHANNEL_0_POSITION	vec2	Top left position of this texture on the atlas in UV coords.
CHANNEL_0_SIZE	vec2	Size of this texture on the atlas in UV coords.
FRAME_SIZE	vec2	Size of sub-rectangle of the texture to be rendered, e.g. the crop (graphic) or animation frame (sprite).
INSTANCE_ID	int	The ID of the current instance, it is a count starting at 0.
SIZE	vec2	The width and height in pixels of the space on the screen being drawn to, e.g. the width and height of a graphic.
TEXTURE_SIZE	vec2	Size of the texture in pixels.
UV	vec2	The interpolates UV coordinates that will be passed to the fragment shader. Ranges from (0,0) top left to (1,1) bottom right. (Equivalent to TEXTURE_COORDS, but read only.)

Outputs (read/write)

Name	Type	Description
CHANNEL_0_ATLAS_OFFSET	vec2	The position on the texture atlas for the texture assigned to channel 0.
CHANNEL_1_ATLAS_OFFSET	vec2	The position on the texture atlas for the texture assigned to channel 1.
CHANNEL_2_ATLAS_OFFSET	vec2	The position on the texture atlas for the texture assigned to channel 2.
CHANNEL_3_ATLAS_OFFSET	vec2	The position on the texture atlas for the texture assigned to channel 3.
CHANNEL_0_TEXTURE_COORDS	vec2	The scaled, interpolated texture coordinates for the texture in channel 0, uses CHANNEL_0_ATLAS_OFFSET.
CHANNEL_1_TEXTURE_COORDS	vec2	The scaled, interpolated texture coordinates for the texture in channel 1, uses CHANNEL_1_ATLAS_OFFSET.
CHANNEL_2_TEXTURE_COORDS	vec2	The scaled, interpolated texture coordinates for the texture in channel 2, uses CHANNEL_2_ATLAS_OFFSET.
CHANNEL_3_TEXTURE_COORDS	vec2	The scaled, interpolated texture coordinates for the texture in channel 3, uses CHANNEL_3_ATLAS_OFFSET.
POSITION	vec2	The position of the entity in screen coords (pixels)
SCALE	vec2	The scale factor of the entity
REF	vec2	The offset reference position of the entity in screen coords (pixels)
FLIP	vec2	The horizontal and vertical flip of the entity. -1 is flipped, 1 is not.
ROTATION	float	The rotation amount in radians to be applied to the current vertex.
TEXTURE_COORDS (Redundant, use UV)	vec2	The interpolates UV coordinates that will be passed to the fragment shader. Ranges from (0,0) top left to (1,1) bottom right. (Equivalent to UV, but modifiable.)

Blend Shader Specific

Outputs (read/write)

Name	Type	Description
SIZE	vec2	The width and height in pixels of the space on the screen being drawn to, e.g. the width and height of a graphic.
UV	vec2	The interpolates UV coordinates. Ranges from (0,0) top left to (1,1) bottom right.

Fragment Shader Programs

Common

Variables (read only)

Name	Type	Description
SIZE	vec2	The width and height in pixels of the space on the screen being drawn to, e.g. the width and height of a graphic.
UV	vec2	The interpolates UV coordinates. Ranges from (0,0) top left to (1,1) bottom right.

Outputs (read/write)

Name	Type	Description
COLOR	vec4	Final pixel color.

Entity Shader Specific

Variables (read only)

Name	Type	Description
ATLAS_SIZE	vec2	Size of the atlas this texture is on, in pixels.
CHANNEL_0	vec4	Pixel color value from texture channel 0.
CHANNEL_1	vec4	Pixel color value from texture channel 1.
CHANNEL_2	vec4	Pixel color value from texture channel 2.
CHANNEL_3	vec4	Pixel color value from texture channel 3.
CHANNEL_0_POSITION	vec2	Top left position of this texture on the atlas in UV coords.
CHANNEL_0_SIZE	vec2	Size of this texture on the atlas in UV coords.
CHANNEL_0_TEXTURE_COORDS	vec2	Scaled texture coordinates.
CHANNEL_1_TEXTURE_COORDS	vec2	Scaled texture coordinates.
CHANNEL_2_TEXTURE_COORDS	vec2	Scaled texture coordinates.
CHANNEL_3_TEXTURE_COORDS	vec2	Scaled texture coordinates.
INSTANCE_ID	int	The ID of the current instance, it is a count starting at 0.
LIGHT_COUNT	int	Total number of lights in the scene.
LIGHT_INDEX	int	Index of the current light starting at 0 with a range of 0 to 7.
ROTATION	float	The rotation amount in radians.
SCREEN_COORDS	vec2	The absolute position of this pixel on the screen.
SRC_CHANNEL	sampler2D	The texture channel for the source image data. Current we only bind one atlas at a time. The 4 channels otherwise mention are all textures on the same atlas. It's a limitation we may remove in the future.
TEXTURE_SIZE	vec2	Size of the texture in pixels.

Outputs (read/write)

Please note that LIGHT_ variables change during execution of the program to show the details of the current light affecting the element being drawn.

Name	Type	Description
LIGHT_ACTIVE	int	Is the light enabled?
LIGHT_ANGLE	float	Used in spotlights to determine the angle of the light cone.
LIGHT_COLOR	vec4	The color of the light.
LIGHT_FALLOFF_TYPE	int	The type of falloff to be used: 0 = none, 1 = smooth linear, 2 = smooth quadtratic, 3 = linear, 4 = quadratic
LIGHT_FAR	float	The maximum distance from the light up to which it will affect the scene.
LIGHT_FAR_CUT_OFF	int	Values are 1 or 0, this is really a boolean that determines if the LIGHT_FAR value is used or not. If not the light will attenuate forever.
LIGHT_INTENSITY	float	The intensity of the light.
LIGHT_NEAR	float	The minimum distance to the light where it will begin to affect the scene.
LIGHT_POSITION	vec2	The light's position.
LIGHT_ROTATION	float	The light's rotation.
LIGHT_SPECULAR	vec4	The specular color of the light.
LIGHT_TYPE	int	What type of light is it? (0 = ambient, 1 = direction, 2 = point, 3 = spot)

Blend Shader Specific

Variables (read only)

Name	Type	Description
DST_CHANNEL	sampler2D	The texture channel for the destination image data.
SRC_CHANNEL	sampler2D	The texture channel for the source image data.

Outputs (read/write)

Name	Type	Description
DST	vec4	Pixel color value from DST texture.
SRC	vec4	Pixel color value from SRC texture.