sample_bias

Live Demo

The sample_bias function reads a texture with an added bias to the automatically computed mip level. This can sharpen or blur the result.

Signature

bwsl

sample_bias :: (texture2D tex, sampler samp, float2 uv, float bias) -> float4 {...}

Parameters

Parameter	Type	Description
`tex`	`texture2D`	The texture to sample
`samp`	`sampler`	Sampler state
`uv`	`float2`	Texture coordinates
`bias`	`float`	LOD bias (negative = sharper, positive = blurrier)

Return Value

Returns the texel value with the biased mip level.

Example

bwsl

pipeline SharpTextures {
  @fragment_only
  fragment {
    // Sample with sharpening bias for distant textures
    float dist = length(input.worldPos - cameraPos);
    float sharpenBias = -0.5;  // Negative = sharper

    // Apply stronger sharpening at distance
    float bias = lerp(0.0, sharpenBias, saturate(dist / 100.0));
    float4 color = sample_bias(resources.albedoTex, resources.linearSampler, input.uv, bias);

    output.color = color;
  }
}

Common Use Cases

Texture Sharpening

bwsl

// Sharpen textures slightly
float4 sharp = sample_bias(resources.tex, resources.linearSampler, uv, -0.5);  // Use lower mip

Distance-Based Blur

bwsl

// Blur distant objects
float blurAmount = saturate(distance / maxDist) * 2.0;
float4 blurred = sample_bias(resources.tex, resources.linearSampler, uv, blurAmount);

Material Roughness Hint

bwsl

// Suggest blurrier appearance for rough materials
float roughnessBias = roughness * 1.5;
float4 diffuse = sample_bias(resources.diffuseTex, resources.linearSampler, uv, roughnessBias);

Anti-Aliasing Adjustment

bwsl

// Reduce aliasing on high-frequency textures
float4 color = sample_bias(resources.detailTex, resources.linearSampler, uv * 10.0, 0.5);

LOD Debugging

bwsl

// Force higher mip levels for testing
float4 debugMip = sample_bias(resources.tex, resources.linearSampler, uv, debugBias);

Bias Values

Negative bias: Uses a smaller mip level (sharper, more aliasing)
Zero bias: Normal automatic LOD selection
Positive bias: Uses a larger mip level (blurrier, less detail)

Fragment Shader Only

sample_bias relies on automatic LOD calculation, which is only available in fragment shaders. Use sample_lod in vertex or compute shaders.

Typical Values

Sharpening: -0.5 to -1.0
Subtle blur: 0.5 to 1.0
Strong blur: 1.0 to 3.0

Compiled Output

When compiled to GLSL:

glsl

texture(tex, uv, bias)

When compiled to HLSL:

hlsl

tex.SampleBias(samplerState, uv, bias)

When compiled to Metal:

metal

tex.sample(sampler, uv, bias(biasValue))

Test sample_bias in a live shader

Live Demo

Signature

Parameters

Return Value

Example

Common Use Cases

Texture Sharpening

Distance-Based Blur

Material Roughness Hint

Anti-Aliasing Adjustment

LOD Debugging

Compiled Output

See Also