Pass nil texture to metal fragment shader

Question

Hello everyone, I am studying apply metal to scenekit.

I want to pass nil texture to fragment shader. But I don't know how...

This code is for pass texture named volume to fragment shader using scntechnique.

swift code

if let path = Bundle.main.path(
      forResource: "volumerendering-metal",
      ofType: "plist")
    {
      if let dico1 = NSDictionary(contentsOfFile: path) {
        let dico = dico1 as! [String: AnyObject]
        let technique = SCNTechnique(dictionary: dico)
         
        let screenSize = NSValue(
          cgSize: view.frame.size.applying(CGAffineTransform(scaleX: 2.0, y: 2.0)))
        technique?.setValue(screenSize,
                  forKeyPath: "screen_size")
         
        technique?.setValue(nil, forKey: "volume")
       // or? 
       // technique?.setObject(nil, forKeyedSubscript: "volume" as NSCopying)
         
        scnView.technique = technique
      }
    }

property list file

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>passes</key>
	<dict>
		<key>pass_backface</key>
		<dict>
			<key>metalVertexShader</key>
			<string>backface_vertex</string>
			<key>metalFragmentShader</key>
			<string>backface_fragment</string>
			<key>program</key>
			<string>doesntexist</string>
			<key>depthStates</key>
			<dict>
				<key>clear</key>
				<true/>
			</dict>
			<key>colorStates</key>
			<dict>
				<key>clear</key>
				<true/>
				<key>clearColor</key>
				<string>sceneBackground</string>
			</dict>
			<key>cullMode</key>
			<string>front</string>
			<key>includeCategoryMask</key>
			<string>2</string>
			<key>draw</key>
			<string>DRAW_NODE</string>
			<key>inputs</key>
			<dict>
				<key>aPos</key>
				<string>vertex-symbol</string>
			</dict>
			<key>outputs</key>
			<dict>
				<key>color</key>
				<string>backface</string>
			</dict>
		</dict>
		<key>pass_mip</key>
		<dict>
			<key>colorStates</key>
			<dict>
				<key>clear</key>
				<true/>
				<key>clearColor</key>
				<string>sceneBackground</string>
			</dict>
			<key>depthStates</key>
			<dict>
				<key>clear</key>
				<true/>
			</dict>
			<key>metalVertexShader</key>
			<string>mip_vertex</string>
			<key>metalFragmentShader</key>
			<string>mip_fragment</string>
			<key>program</key>
			<string>doesntexist</string>
			<key>cullMode</key>
			<string>back</string>
			<key>includeCategoryMask</key>
			<string>2</string>
			<key>draw</key>
			<string>DRAW_NODE</string>
			<key>inputs</key>
			<dict>
				<key>aPos</key>
				<string>vertex-symbol</string>
				<key>viewport</key>
				<string>screen_size</string>
				<key>backface</key>
				<string>backface</string>
				<key>volume</key>
				<string>volume</string>
			</dict>
			<key>outputs</key>
			<dict>
				<key>color</key>
				<string>COLOR</string>
				<key>depth</key>
				<string>DEPTH</string>
			</dict>
		</dict>
	</dict>
	<key>sequence</key>
	<array>
		<string>pass_backface</string>
		<string>pass_mip</string>
	</array>
	<key>targets</key>
	<dict>
		<key>backface</key>
		<dict>
			<key>type</key>
			<string>color</string>
		</dict>
	</dict>
	<key>symbols</key>
	<dict>
		<key>vertex-symbol</key>
		<dict>
			<key>semantic</key>
			<string>vertex</string>
		</dict>
		<key>screen_size</key>
		<dict>
			<key>type</key>
			<string>vec2</string>
		</dict>
		<key>volume</key>
		<dict>
			<key>type</key>
			<string>sampler3D</string>
		</dict>
	</dict>
</dict>
</plist>

shader code

fragment float4 mip_fragment
(
  VertexOutput in [[stage_in]]
  , texture2d<float, access::sample> backface [[texture(0)]]
  , texture2d<float, access::sample> volume [[texture(1)]]
)
{
  ...  
  if (is_null_texture(volume)) return float4(1, 0, 0, 0);
  else return float4(0, 1, 0, 0);
}

I want to get red object but green object.... Because I want to set 3d texture at runtime. So before set it want to be nil, because error occurred. (https://developer.apple.com/forums/thread/688841)

445

Posted by

Wonki

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Add a Comment

Answer 1

I’m not an expert on SceneKit, but why do you have volume as type sampler3D in your plist, and volume as a texture2D in your shader? If you want it to be a texture3D, it should probably be set to that in your shader and plist.

Posted by

Graphics and Games Engineer

sorry for my mistake texture3d in shader is right. I am checking when use 2d texture, whether error occurred or not. when use 3d texture, error occurred, but 2d texture doesn't. So I want to pass nil when using 3d texture for first and set texture at runtime.

error : Fragment Function(mip_fragment): incorrect type of texture (MTLTextureType2D) bound at texture binding at index 1 (expect MTLTextureType3D) for volume[0].

—
Wonki
No problem, are you able to post your entire project on GitHub or another site? It would be nice to see the full source code to better solve the problem.

—
Graphics and Games Engineer
Yeah, I working on my corporation git repository now. So I gonna set my own public repository for this work and upload link at follow comment.

—
Wonki

Answer 2

Yes,

this shader code is right.

fragment float4 mip_fragment
(
  VertexOutput in [[stage_in]]
  , texture2d<float, access::sample> backface [[texture(0)]]
  , texture3d<float, access::sample> volume [[texture(1)]]
)
{
  ...  
  if (is_null_texture(volume)) return float4(1, 0, 0, 0);
  else return float4(0, 1, 0, 0);
}

And I check now, is_null_texture makes same error like volume.sample function.

Posted by

Wonki

Add a Comment

Answer 3

https://bitbucket.org/skia_wonki/metal-volume-rendering/src/master/

This is full source of question.

Posted by

Wonki

Add a Comment

Pass nil texture to metal fragment shader

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