CanvasItem shaders

CanvasItem shaders are used to draw all 2D elements in Godot. These include all nodes that inherit from CanvasItems, and all GUI elements.

CanvasItem shaders contain less built-in variables and functionality than Spatial shaders, but they maintain the same basic structure with vertex, fragment, and light processor functions.

Render modes

Render mode Description
blend_mix Mix blend mode (alpha is transparency), default.
blend_add Additive blend mode.
blend_sub Subtractive blend mode.
blend_mul Multiplicative blend mode.
blend_premul_alpha Pre-multiplied alpha blend mode.
blend_disabled Disable blending, values (including alpha) are written as-is.
unshaded Result is just albedo. No lighting/shading happens in material.
light_only Only draw on light pass.
skip_vertex_transform VERTEX/NORMAL/etc need to be transformed manually in vertex function.

Vertex built-ins

Values marked as “in” are read-only. Values marked as “out” are for optional writing and will not necessarily contain sensible values. Values marked as “inout” provide a sensible default value, and can optionally be written to. Samplers are not subjects of writing and they are not marked.

Vertex data (VERTEX) is presented in local space (pixel coordinates, relative to the camera). If not written to, these values will not be modified and be passed through as they came.

The user can disable the built-in modelview transform (projection will still happen later) and do it manually with the following code:

shader_type canvas_item;
render_mode skip_vertex_transform;

void vertex() {

    VERTEX = (EXTRA_MATRIX * (WORLD_MATRIX * vec4(VERTEX, 0.0, 1.0))).xy;
}

Note

WORLD_MATRIX is actually a modelview matrix. It takes input in local space and transforms it into view space.

In order to get the world space coordinates of a vertex, you have to pass in a custom uniform like so:

material.set_shader_param("global_transform", get_global_transform())

Then, in your vertex shader:

uniform mat4 global_transform;
varying vec2 world_position;

void vertex(){
    world_position = (global_transform * vec4(VERTEX, 0.0, 1.0)).xy;
}

world_position can then be used in either the vertex or fragment functions.

Other built-ins, such as UV and COLOR, are also passed through to the fragment function if not modified.

For instancing, the INSTANCE_CUSTOM variable contains the instance custom data. When using particles, this information is usually:

  • x: Rotation angle in radians.
  • y: Phase during lifetime (0 to 1).
  • z: Animation frame.
Built-in Description
in mat4 WORLD_MATRIX Image space to view space transform.
in mat4 EXTRA_MATRIX Extra transform.
in mat4 PROJECTION_MATRIX View space to clip space transform.
in float TIME Global time, in seconds.
in vec4 INSTANCE_CUSTOM Instance custom data.
in bool AT_LIGHT_PASS True if this is a light pass.
inout vec2 VERTEX Vertex, in image space.
in vec2 TEXTURE_PIXEL_SIZE Normalized pixel size of default 2D texture. For a Sprite with a texture of size 64x32px, TEXTURE_PIXEL_SIZE = vec2(1/64, 1/32)
inout vec2 UV UV.
inout vec4 COLOR Color from vertex primitive.
inout float POINT_SIZE Point size for point drawing.

Fragment built-ins

Certain Nodes (for example, Sprites) display a texture by default. However, when a custom fragment function is attached to these nodes, the texture lookup needs to be done manually. Godot does not provide the texture color in the COLOR built-in variable; to read the texture color for such nodes, use:

COLOR = texture(TEXTURE, UV);

This differs from the behaviour of the built-in normal map. If a normal map is attached, Godot uses it by default and assigns its value to the built-in NORMAL variable. If you are using a normal map meant for use in 3D, it will appear inverted. In order to use it in your shader, you must assign it to the NORMALMAP property. Godot will handle converting it for use in 2D and overwriting NORMAL.

NORMALMAP = texture(NORMAL_TEXTURE, UV).rgb;
Built-in Description
in vec4 FRAGCOORD Fragment coordinate, pixel adjusted.
inout vec3 NORMAL Normal read from NORMAL_TEXTURE. Writable.
out vec3 NORMALMAP Configures normal maps meant for 3D for use in 2D. If used, overwrites NORMAL.
inout float NORMALMAP_DEPTH Normalmap depth for scaling.
in vec2 UV UV from vertex function.
inout vec4 COLOR Color from vertex function and output fragment color. If unused, will be set to TEXTURE color.
in sampler2D TEXTURE Default 2D texture.
in sampler2D NORMAL_TEXTURE Default 2D normal texture.
in vec2 TEXTURE_PIXEL_SIZE Normalized pixel size of default 2D texture. For a Sprite with a texture of size 64x32px, TEXTURE_PIXEL_SIZE = vec2(1/64, 1/32)
in vec2 SCREEN_UV Screen UV for use with SCREEN_TEXTURE.
in vec2 SCREEN_PIXEL_SIZE Size of individual pixels. Equal to inverse of resolution.
in vec2 POINT_COORD Coordinate for drawing points.
in float TIME Global time in seconds.
in bool AT_LIGHT_PASS True if this is a light pass.
in sampler2D SCREEN_TEXTURE Screen texture, mipmaps contain gaussian blurred versions.

Light built-ins

Light processor functions work differently in 2D than they do in 3D. In CanvasItem shaders, the shader is called once for the object being drawn, and then once for each light touching that object in the scene. Use render_mode unshaded if you do not want any light passes to occur for that object. Use render_mode light_only if you only want light passes to occur for that object; this can be useful when you only want the object visible where it is covered by light.

When the shader is on a light pass, the AT_LIGHT_PASS variable will be true.

Built-in Description
in vec4 FRAGCOORD Fragment coordinate of pixel center. Origin at lower left.
in vec3 NORMAL Input Normal. Although this value is passed in, normal calculation still happens outside of this function.
in vec2 UV UV from vertex function, equivalent to the UV in the fragment function.
in vec4 COLOR Input Color. This is the output of the fragment function with final modulation applied.
sampler2D TEXTURE Current texture in use for CanvasItem.
in vec2 TEXTURE_PIXEL_SIZE Normalized pixel size of default 2D texture. For a Sprite with a texture of size 64x32px, TEXTURE_PIXEL_SIZE = vec2(1/64, 1/32)
in vec2 SCREEN_UV SCREEN_TEXTURE Coordinate (for using with screen texture).
in vec2 POINT_COORD UV for Point Sprite.
in float TIME Global time in seconds.
inout vec2 LIGHT_VEC Vector from light to fragment, can be modified to alter shadow computation.
inout float LIGHT_HEIGHT Height of Light. Only effective when normals are used.
inout vec4 LIGHT_COLOR Color of Light.
in vec2 LIGHT_UV UV for Light texture.
out vec4 SHADOW_COLOR Shadow Color of Light.
inout vec4 LIGHT Value from the Light texture and output color. Can be modified. If not used, the light function is ignored.