Blending is used to make transparent objects.
When graphics are rendered, after all shaders have executed and all textures have been applied, the pixels are written to the screen. How they are combined with what is already there is controlled by the Blend command.
Blend Off
: Turn off blending
Blend SrcFactor DstFactor
: Configure & enable blending. The generated color is multiplied by the SrcFactor. The color already on screen is multiplied by DstFactor and the two are added together.
Blend SrcFactor DstFactor, SrcFactorA DstFactorA
: Same as above, but use different factors for blending the alpha channel.
BlendOp BlendOp
: Instead of adding blended colors together, do a different operation on them.
The following blend operations can be used:
Add | Add source and destination together. |
Sub | Subtract source from destination. |
RevSub | Subtract destination from source. |
Min | Use the smaller of source and destination. |
Max | Use the larger of source and destination. |
LogicalClear | Logical operation: Clear (0) DX11.1 only. |
LogicalSet | Logical operation: Set (1) DX11.1 only. |
LogicalCopy | Logical operation: Copy (s) DX11.1 only. |
LogicalCopyInverted | Logical operation: Copy inverted (!s) DX11.1 only. |
LogicalNoop | Logical operation: Noop (d) DX11.1 only. |
LogicalInvert | Logical operation: Invert (!d) DX11.1 only. |
LogicalAnd | Logical operation: And (s & d) DX11.1 only. |
LogicalNand | Logical operation: Nand !(s & d) DX11.1 only. |
LogicalOr | Logical operation: Or (s |d) DX11.1 only. |
LogicalNor | Logical operation: Nor !(s |d) DX11.1 only. |
LogicalXor | Logical operation: Xor (s ^ d) DX11.1 only. |
LogicalEquiv | Logical operation: Equivalence !(s ^ d) DX11.1 only. |
LogicalAndReverse | Logical operation: Reverse And (s & !d) DX11.1 only. |
LogicalAndInverted | Logical operation: Inverted And (!s & d) DX11.1 only. |
LogicalOrReverse | Logical operation: Reverse Or (s |!d) DX11.1 only. |
LogicalOrInverted | Logical operation: Inverted Or (!s |d) DX11.1 only. |
All following properties are valid for both SrcFactor & DstFactor in the Blend command. Source refers to the calculated color, Destination is the color already on the screen. The blend factors are ignored if BlendOp is using logical operations.
One | The value of one - use this to let either the source or the destination color come through fully. |
Zero | The value zero - use this to remove either the source or the destination values. |
SrcColor | The value of this stage is multiplied by the source color value. |
SrcAlpha | The value of this stage is multiplied by the source alpha value. |
DstColor | The value of this stage is multiplied by frame buffer source color value. |
DstAlpha | The value of this stage is multiplied by frame buffer source alpha value. |
OneMinusSrcColor | The value of this stage is multiplied by (1 - source color). |
OneMinusSrcAlpha | The value of this stage is multiplied by (1 - source alpha). |
OneMinusDstColor | The value of this stage is multiplied by (1 - destination color). |
OneMinusDstAlpha | The value of this stage is multiplied by (1 - destination alpha). |
Below are the most common blend types:
Blend SrcAlpha OneMinusSrcAlpha // Alpha blending
Blend One One // Additive
Blend OneMinusDstColor One // Soft Additive
Blend DstColor Zero // Multiplicative
Blend DstColor SrcColor // 2x Multiplicative
Here is a small example shader that adds a texture to whatever is on the screen already:
Shader "Simple Additive" {
Properties {
_MainTex ("Texture to blend", 2D) = "black" {}
}
SubShader {
Tags { "Queue" = "Transparent" }
Pass {
Blend One One
SetTexture [_MainTex] { combine texture }
}
}
}
And a more complex one, Glass. This is a two-pass shader:
Shader "Glass" {
Properties {
_Color ("Main Color", Color) = (1,1,1,1)
_MainTex ("Base (RGB) Transparency (A)", 2D) = "white" {}
_Reflections ("Base (RGB) Gloss (A)", Cube) = "skybox" { TexGen CubeReflect }
}
SubShader {
Tags { "Queue" = "Transparent" }
Pass {
Blend SrcAlpha OneMinusSrcAlpha
Material {
Diffuse [_Color]
}
Lighting On
SetTexture [_MainTex] {
combine texture * primary double, texture * primary
}
}
Pass {
Blend One One
Material {
Diffuse [_Color]
}
Lighting On
SetTexture [_Reflections] {
combine texture
Matrix [_Reflection]
}
}
}
}