<p>You havent' set the <code>mipFilter</code> property for your <code>samplerDescriptor</code>.  The default value for <code>mipFilter</code> is <code>notMipped</code> which means the sampler will never access anything other than level 0. Set it to <code>nearest</code> or <code>linear</code>.</p>

CC BY-SA 3.0
2018-01-24T17:01:02.543Z
2018-01-24T17:01:02.543Z
GroverManheim
<p>I have a source texture (480x480) that was created with mipmapped set to true (error checking removed to simply this post), and a dest texture (100x100):</p>

<pre><code>// source texture
var textureDescriptor = MTLTextureDescriptor.texture2DDescriptor(pixelFormat: MTLPixelFormat.r8Unorm, width: Int(480), height: Int(480), mipmapped: true)
textureDescriptor.usage = .unknown // .shaderWrite .shaderRead
srcTexture = metalDevice!.makeTexture(descriptor: textureDescriptor)
// Dest texture
textureDescriptor = MTLTextureDescriptor.texture2DDescriptor(pixelFormat: MTLPixelFormat.r8Unorm, width: Int(100), height: Int(100), mipmapped: false)
textureDescriptor.usage = .shaderWrite
destTexture = metalDevice!.makeTexture(descriptor: textureDescriptor)
</code></pre>

<p>The sampler is defined:</p>

<pre><code>let samplerDescriptor = MTLSamplerDescriptor()
samplerDescriptor.magFilter = .linear
samplerDescriptor.minFilter = .linear
samplerDescriptor.rAddressMode = .clampToZero
samplerDescriptor.sAddressMode = .clampToZero
samplerDescriptor.tAddressMode = .clampToZero
samplerDescriptor.normalizedCoordinates = true
textureSampler = metalDevice!.makeSamplerState(descriptor: samplerDescriptor)
</code></pre>

<p>I populated the src texture with an image.</p>

<p>Then generated the mipmaps:</p>

<pre><code>let blitEncoder = metalCommandBuffer!.makeBlitCommandEncoder()
blitEncoder!.pushDebugGroup("Dispatch mipmap kernel")
blitEncoder!.generateMipmaps(for: srcTexture!);
blitEncoder!.popDebugGroup()
blitEncoder!.endEncoding()
</code></pre>

<p>And in the same command buffer, ran the resize kernel:</p>

<pre><code>let computeEncoder = metalCommandBuffer!.makeComputeCommandEncoder()
computeEncoder!.pushDebugGroup("Dispatch resize image kernel")
computeEncoder!.setComputePipelineState(resizeImagePipeline)
computeEncoder!.setTexture(srcTexture, index: 0)
computeEncoder!.setTexture(destTexture, index: 1)
computeEncoder!.setSamplerState(textureSampler, index: 0)
let threadGroupCount = MTLSizeMake(20, 10, 1)
let threadGroups = MTLSizeMake(destTexture!.width / threadGroupCount.width, destTexture!.height / threadGroupCount.height, 1)
computeEncoder!.dispatchThreadgroups(threadGroups, threadsPerThreadgroup: threadGroupCount)
computeEncoder!.popDebugGroup()
computeEncoder!.endEncoding()
</code></pre>

<p>The compute kernel is (remember, this is not a fragment shader which would automatically know how to set the mipmap level of detail):</p>

<pre><code>kernel void resizeImage(
texture2d&lt;half, access::sample&gt; sourceTexture [[texture(0)]],
texture2d&lt;half, access::write&gt; destTexture [[texture(1)]],
sampler samp [[sampler(0)]],
uint2 gridPosition [[thread_position_in_grid]])
{
float2 srcSize = float2(sourceTexture.get_width(0),
sourceTexture.get_height(0));
float2 destSize = float2(destTexture.get_width(0),
destTexture.get_height(0));
float2 sourceCoords = float2(gridPosition) / destSize;
/*+ The following attempts all produced a pixelated image
(no edges smoothed out like a fragment shader would)
half4 color = sourceTexture.sample(samp, sourceCoords);
float lod = srcSize.x / destSize.x;
float lod = 0.0;
float lod = 1.0;
float lod = 2.0;
float lod = 3.0;
float lod = 4.0;
float lod = 4.5;
float lod = 5.0;
float lod = 5.5;
*/
float lod = 6.0;
half4 color = sourceTexture.sample(samp, sourceCoords, level(lod));
destTexture.write(color, gridPosition);
}
</code></pre>

<p>No matter what lod is set to, I get the same exact pixelated results. Why won't the mipmapping work?
Thanks for any help you can provide.</p>

<compute-shader><mipmap><metal>
Mipmap sampler in Metal compute kernel (not vertex or fragment shader)
Labeno
# Mipmap sampler in Metal compute kernel (not vertex or fragment shader)

(Asked by: username_0 on 2018-01-15)

I have a source texture (480x480) that was created with mipmapped set to true (error checking removed to simply this post), and a dest texture (100x100):

```
// source texture
var textureDescriptor = MTLTextureDescriptor.texture2DDescriptor(pixelFormat: MTLPixelFormat.r8Unorm, width: Int(480), height: Int(480), mipmapped: true)
textureDescriptor.usage = .unknown // .shaderWrite .shaderRead
srcTexture = metalDevice!.makeTexture(descriptor: textureDescriptor)
// Dest texture
textureDescriptor = MTLTextureDescriptor.texture2DDescriptor(pixelFormat: MTLPixelFormat.r8Unorm, width: Int(100), height: Int(100), mipmapped: false)
textureDescriptor.usage = .shaderWrite
destTexture = metalDevice!.makeTexture(descriptor: textureDescriptor)

```

The sampler is defined:

```
let samplerDescriptor = MTLSamplerDescriptor()
samplerDescriptor.magFilter = .linear
samplerDescriptor.minFilter = .linear
samplerDescriptor.rAddressMode = .clampToZero
samplerDescriptor.sAddressMode = .clampToZero
samplerDescriptor.tAddressMode = .clampToZero
samplerDescriptor.normalizedCoordinates = true
textureSampler = metalDevice!.makeSamplerState(descriptor: samplerDescriptor)

```

I populated the src texture with an image.

Then generated the mipmaps:

```
let blitEncoder = metalCommandBuffer!.makeBlitCommandEncoder()
blitEncoder!.pushDebugGroup("Dispatch mipmap kernel")
blitEncoder!.generateMipmaps(for: srcTexture!);
blitEncoder!.popDebugGroup()
blitEncoder!.endEncoding()

```

And in the same command buffer, ran the resize kernel:

```
let computeEncoder = metalCommandBuffer!.makeComputeCommandEncoder()
computeEncoder!.pushDebugGroup("Dispatch resize image kernel")
computeEncoder!.setComputePipelineState(resizeImagePipeline)
computeEncoder!.setTexture(srcTexture, index: 0)
computeEncoder!.setTexture(destTexture, index: 1)
computeEncoder!.setSamplerState(textureSampler, index: 0)
let threadGroupCount = MTLSizeMake(20, 10, 1)
let threadGroups = MTLSizeMake(destTexture!.width / threadGroupCount.width, destTexture!.height / threadGroupCount.height, 1)
computeEncoder!.dispatchThreadgroups(threadGroups, threadsPerThreadgroup: threadGroupCount)
computeEncoder!.popDebugGroup()
computeEncoder!.endEncoding()

```

The compute kernel is (remember, this is not a fragment shader which would automatically know how to set the mipmap level of detail):

```
kernel void resizeImage(
texture2d<half, access::sample> sourceTexture [[texture(0)]],
texture2d<half, access::write> destTexture [[texture(1)]],
sampler samp [[sampler(0)]],
uint2 gridPosition [[thread_position_in_grid]])
{
float2 srcSize = float2(sourceTexture.get_width(0),
sourceTexture.get_height(0));
float2 destSize = float2(destTexture.get_width(0),
destTexture.get_height(0));
float2 sourceCoords = float2(gridPosition) / destSize;
/*+ The following attempts all produced a pixelated image
(no edges smoothed out like a fragment shader would)
half4 color = sourceTexture.sample(samp, sourceCoords);
float lod = srcSize.x / destSize.x;
float lod = 0.0;
float lod = 1.0;
float lod = 2.0;
float lod = 3.0;
float lod = 4.0;
float lod = 4.5;
float lod = 5.0;
float lod = 5.5;
*/
float lod = 6.0;
half4 color = sourceTexture.sample(samp, sourceCoords, level(lod));
destTexture.write(color, gridPosition);
}

```

No matter what lod is set to, I get the same exact pixelated results. Why won't the mipmapping work?
Thanks for any help you can provide.

**Tags:** compute-shader, mipmap, metal


---

## 1 answers

### Answer by username_1 on 2018-01-24. Score: 2

You havent' set the `mipFilter` property for your `samplerDescriptor`. The default value for `mipFilter` is `notMipped` which means the sampler will never access anything other than level 0. Set it to `nearest` or `linear`.


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