Custom Effects

Vizard 7 » Reference » Shaders » Effects » Custom Effects

7.7

Custom Effects

The effect framework makes it easy to write custom shader code that combines with existing shaders. There is no need to re-implement the entire shader pipeline anymore (vertex transformation, lighting, fog, etc..). You just write a few lines of code and Vizard will automatically combine it with existing effects to generate the full shader.

Effect Syntax

Shader effects are defined using a simple syntax (sections within brackets [] are optional):

Effect [Name] {

    [Properties]

    Shader {
        [Units]
    }
}

[Name]

This is an optional string that allows assigning an arbitrary name to the effect. The name does not affect the functionality, but can be accessed in the script using the <effect>.getName command.

[Properties]

This section allows defining optional properties and input uniforms of the effect.

Type

Type "name"

This declares the type of the effect. The type name can be an arbitrary string. When Vizard generates the full shader code using all the applied effects, it will only use one effect per unique type name. This allows both the use of multiple effects by using different type names and the ability to override existing effects by using the same type name. If no type is specified, then default will be used. The built-in generated material effects use the default type name, so it is recommended to use the default type if you want to use the effect to set the base material values. The effect type name can be accessed in the script using the <effect>.getTypeName command.

The table below lists some type names used by other built-in effects. You can use these type names if you wish to override the corresponding effect:

Type	Descripton
AmbientLight	Used by the default ambient light effect. Use this type name if you wish to create a custom ambient lighting model.
LightingModel	Used by the default lighting model effect. Use this type name if you wish to create a custom lighting model.
Fog	Used by the default fog effect. Use this type name if you wish to create a custom fog effect.

Texture2D

Texture2D "name" {
[coordUnit 0]
[unit -1]
}

Creates a 2D texture property.

name: The name to use for the texture uniform. Must be a valid shader uniform name.
coordUnit: The texture coordinate unit to assign to the texture. If the value is greater than or equal to 0, then the UV coordinates for the texture can be accessed within the shader code using the uv<name> variable, where <name> is the property name. If the value is -1, then no UV coordinates are assigned to the texture, and it is assumed the UV coordinates are dynamically generated within the shader.
unit: The texture unit to assign to the texture property. If the value is greater than or equal to 0, then the effect will use whatever texture is already assigned on that unit. If the value is -1, then the effect will assume that either the texture uniform is manually applied or that the texture is specified using the <effect>.setProperty command.

TextureCube

TextureCube "name" {
[coordUnit -1]
[unit -1]
}

Creates a cubemap texture property.

name: The name to use for the texture uniform. Must be a valid shader uniform name.
coordUnit: The texture coordinate unit to assign to the texture. If the value is greater than or equal to 0, then the UV coordinates for the texture can be accessed within the shader code using the uv<name> variable, where <name> is the property name. If the value is -1, then no UV coordinates are assigned to the texture, and it is assumed the UV coordinates are dynamically generated within the shader.
unit: The texture unit to assign to the texture property. If the value is greater than or equal to 0, then the effect will use whatever texture is already assigned on that unit. If the value is -1, then the effect will assume that either the texture uniform is manually applied or that the texture is specified using the <effect>.setProperty command.

Float

Float "name" {
[value x y z w]
}

Creates a float property.

name: The name to use for the float uniform. Must be a valid shader uniform name.
value: A space-delimited list specifying the default float values. The length of the list determines the type of the uniform (1=float, 2=vec2, 3=vec3, 4=vec4). The value can be modified in script using the <effect>.setProperty command. If not specified, it will default to a single value of 0.

Int

Int "name" {
[value x y z w]
}

Creates an integer property.

name: The name to use for the integer uniform. Must be a valid shader uniform name.
value: A space-delimited list specifying the default integer values. The length of the list determines the type of the uniform (1=int, 2=ivec2, 3=ivec3, 4=ivec4). The value can be modified in script using the <effect>.setProperty command. If not specified, it will default to a single value of 0.

Bool

Bool "name" {
[value x y z w]
}

Creates a boolean property.

name: The name to use for the boolean uniform. Must be a valid shader uniform name.
value: A space-delimited list specifying the default boolean values. The length of the list determines the type of the uniform (1=bool, 2=bvec2, 3=bvec3, 4=bvec4). The value can be modified in script using the <effect>.setProperty command. If not specified, it will default to a single value of 0.

Matrix

Matrix2 "name" {
    [value v1 v2 v3 v4]
}

Matrix3 "name" {
    [value v1 v2 v3 ... v9]
}

Matrix4 "name" {
    [value v1 v2 v3 ... v16]
}

Creates a matrix property.

name: The name to use for the matrix uniform. Must be a valid shader uniform name.
value: A space-delimited list specifying the default matrix values. The length depends on the type of matrix specified (Matrix2=4, Matrix3=9, Matrix4=16). The value can be modified in script using the <effect>.setProperty command.

TangentCoordUnit

TangentCoordUnit unit

This declares the texture coordinate unit to use to generate tangent/binormal values for bump mapping. This should only be specified if a tangent space normal map is being used by the effect.

[Units]

This section is where the actual shader code is defined for the effect. Multiple shader units can be defined, allowing an effect to insert code into multiple stages of the shader pipeline. Each shader unit is defined using the following syntax:

BEGIN Name
Code
END

Name

The section name of the shader pipeline to insert the code into. The default effect composer created by the vizfx library provides the following sections for inserting code into:

Name	Shader	Description
FragmentHeader	Fragment	Allows declaring optional functions or varying/uniform inputs for the fragment shader.
FragmentInit	Fragment	Called at the beginning of the fragment shader. Can be used to discard fragments based on custom clip volumes.
Material	Fragment	Material properties of the pixel are applied to the material structure m. The material structure contains the following fields: vec3 diffuse vec3 specular vec3 emission vec3 normal float shininess float alpha
PostMaterial	Fragment	Post-processing of material properties can be applied to the material structure m.
Ambient	Fragment	Global ambient color is added to g.ambient variable.
Lighting	Fragment	Lighting is applied here to the light structure light. The light structure contains the following fields: vec3 direction vec3 color float attenuation Once the light fields are set, the light must be applied using the following code: vizfx_AddLight(light);
DiffuseModel	Fragment	Global diffuse light color is added to g.diffuse variable. This is called once for each light within a separate function that takes as input the material structure m, light structure l, and view direction viewDir.
SpecularModel	Fragment	Global specular light color is added to g.specular variable. This is called once for each light within a separate function that takes as input the material structure m, light structure l, and view direction viewDir.
FinalColor	Fragment	Called at the end of the fragment shader to allow making adjustments to the final pixel color by modifying the gl_FragColor value.
VertexHeader	Vertex	Allows declaring optional functions or varying/uniform inputs for the vertex shader.
PreTransform	Vertex	Called before the vertex data is transformed by the ModelViewProjection matrix. The following vertex values can be modified: vec4 eyeVertex vec3 eyeNormal vec4 eyeTangent // Only if VIZFX_TANGENT_SPACE is defined
PostTransform	Vertex	Called after vertex data is transformed by the ModelViewProjection matrix.

Code

The actual shader code to insert into the specified section of the shader pipeline. See the table above for variables that can be accessed/modified for each stage. Additionally, the default effect composer created by the vizfx library provides the following commonly used values:

Name	Type	Description
viewDir	vec3	Normalized direction vector of vertex/pixel to view. This will be in the same coordinate system as the material normal vector (m.normal) and the light direction vector (light.direction). The coordinate system may be in eye space or tangent space, depending on whether VIZFX_TANGENT_SPACE is defined.
vizfx_VertexColor	vec4	The vertex/material color.
vizfx_ViewDistance	float	Distance between the view and vertex/pixel.
vizfx_WorldViewDir	vec3	Normalized direction vector of the vertex/pixel to view in world coordinates.
vizfx_WorldPos	vec3	Position of vertex/pixel in world coordinates.
vizfx_WorldNormal	vec3	Normalized normal vector of vertex/pixel in world coordinates.
vizfx_WorldReflect	vec3	Normalized view/normal reflection vector in world coordinates.
vizfx_EyeViewDir	vec3	Normalized direction vector of the vertex/pixel to view in eye coordinates.
vizfx_EyePos	vec3	Position of vertex/pixel in eye coordinates.
vizfx_EyeNormal	vec3	Normalized normal vector of vertex/pixel in eye coordinates.
vizfx_EyeReflect	vec3	Normalized view/normal reflection vector in eye coordinates.
vizfx_ScreenPos	vec2	Position of pixel in normalized screen coordinates.
vizfx_PixelPos	vec2	Position of pixel in viewport coordinates.
vizfx_CubeNormal	vec3	World normal vector in cubemap texture coordinates.
vizfx_CubeReflect	vec3	World reflection vector in cubemap texture coordinates.
vizfx_SphereReflect	vec2	2D sphere map texture coordinates.
vizfx_TangentWorldMatrix	mat3	Matrix to convert tangent space vector to world coordinates.
vizfx_TangentEyeMatrix	mat3	Matrix to convert tangent space vector to eye coordinates.
VIZFX_TANGENT_SPACE	#define	Defined when the shader normal is in tangent space coordinates.
VIZFX_LIGHTING	#define	Defined when lighting is enabled.
VIZFX_FOG	#define	Defined when fog is enabled.

Effect Commands

The viz.addEffect command is used to load an effect from code or a file. Here we load an effect from code:

code = """
Effect {
    Shader {
        BEGIN Material
        m.diffuse = vizfx_VertexColor.rgb;
        END
    }
}
"""
effect = viz.addEffect(code)

Once an effect is created, it can be applied to a model using the <node>.apply command:

model.apply(effect)

The effect can also be added to a composer object. All objects with the composer applied, will also inherit the effect. If an effect of the same type is added to an object and the composer, the effect applied to the object will take precedence over the effect added to the composer. Here we add an effect to the default composer of the vizfx library:

vizfx.getComposer().addEffect(effect)

Effects can be dynamically disabled and enabled using the <effect>.setEnabled command. Effects are enabled by default. Here we disable an effect:

effect.setEnabled(False)

The <effect>.setProperty command can be used to dynamically change the value of an effect property. For example, the following effect defines a MyColor property that is initialized to white. After the effect is loaded, the property value is changed to red.

code = """
Effect {
    Float MyColor {
        value 1 1 1
    }
    Shader {
        BEGIN Material
        m.diffuse = MyColor;
        END
    }
}
"""
effect = viz.addEffect(code)
effect.setProperty('MyColor', viz.RED)

The above code changes the color for all objects using the effect. However, effect properties can be overridden on a per model basis. Using the <node>.setUniformFloat command, we can override the effect property value with a custom value:

code = """
Effect {
    Float MyColor {
        value 1 1 1
    }
    Shader {
        BEGIN Material
        m.diffuse = MyColor;
        END
    }
}
"""
effect = viz.addEffect(code)

# Model will inherit MyColor property value from effect
model_1.apply(effect)

# Model will override MyColor property value with green color
model_2.apply(effect)
model_2.setUniformFloat('MyColor', viz.GREEN)

An effect can be unapplied from all previous nodes and composers using the <effect>.unapply command:

model.apply(effect)
.
.
.

# Will no longer affect the model
effect.unapply()

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