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Upcoming Developments with Metal Ray Tracing
I have watched the Enhance Your App with Metal Ray Tracing video ( wwdc21-10149 ) a few times and am very interested in many of the upcoming features described. It seems as though there will be some tweaks ( ie. Instance IDs ) and some major additions ( ie. Keyframe Animation ). I am wondering if there is any sense of the timing of these features becoming available ( beta or otherwise ) and also, if some of the sample code might be provided in Swift. Thanks so much for the work that went into the video and explanations.
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Jun ’21
Loading an HDR Image into a Metal Texture
I am working on implementing Image Based Lighting in a ray tracing project. In order to get the sampling to work predictably, I will need to load and process an HDR image into a MTLTexture. While using a MTKTextureLoader to load .jpg and .png files has been super-smooth, loading a .hdr file in Swift seems to have a few barriers. I have tried to follow the Processing HDR Images with Metal sample code [ Objective C ], but it relies on some finessing of pointers that I can't duplicate in Swift. Is there currently a best way to move an HDR image into a Metal texture using Swift? Thanks so much!
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1.7k
Jan ’21
Filling in a MTLAccelerationStructureInstanceDescriptor
While translating the Accelerating Ray Tracing Using Metal sample project into Swift, I have run into an issue within the createAccelerationStructures function. I am trying to fill in the first three rows of the instance transformation matrix. In the Objective C example, it looks like: for (int column = 0; column < 4; column++) &#9;for (int row = 0; row < 3; row++) &#9;&#9;instanceDescriptors[instanceIndex].transformationMatrix.columns[column][row] = instance.transform.columns[column][row]; The matrix targeted is a MTLPackedFloat4x3. It has defied me pulling out the needed elements from my instance transform and placing them in the descriptor. I have tried the obvious: for column in 0..<( 4 ) &#9;{ &#9;for row in 0..<( 3 ) &#9;&#9;{ &#9;&#9;anInstanceDescriptorPointer.pointee.transformationMatrix.columns[column][row] = aNodeInstance.transform.columns[column][row] &#9;&#9;} &#9;} I have tried more obscure ideas related to simd matrices and Swift. The compiler errors generally warn me that MTLPackedFloat4x3 has no subscripts. Question - Is there an accepted way to assign three rows from the instance transform to the descriptor transformationMatrix in Swift? Thank you for your earlier help with all of this. I should mention that the new intersector feature in Metal has worked really well for me when feeding it a primitiveaccelerationstructure. Very elegant! But using instances seems to offer more flexibility going forward. Thank you very much!
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Jul ’20
Trying the 'Discover Ray Tracing' Sample Code in Swift
I have enjoyed looking through the 'Discover Ray Tracing with Metal' video and Sample Code. While trying to recreate the Project in Swift, I have run across an issue with setting up an MTLPrimativeAccelerationStructureDescriptor. In Renderer.mm ( Objective C ), within the createAccelerationStructures function, a loop is created: // Create a primitive acceleration structure for each piece of geometry in the scene &#9;for (NSUInteger i = 0; i < _scene.geometries.count; i++) { &#9;Geometry *mesh = _scene.geometries[i]; &#9;MTLAccelerationStructureGeometryDescriptor *geometryDescriptor = [mesh geometryDescriptor]; &#9;// Assign each piece of geometry a consecutive slot in the intersection function table         geometryDescriptor.intersectionFunctionTableOffset = i; &#9;// Create a primitive acceleration structure descriptor to contain the single piece of acceleration structure geometry &#9;MTLPrimitiveAccelerationStructureDescriptor *accelDescriptor = [MTLPrimitiveAccelerationStructureDescriptor descriptor]; &#9;accelDescriptor.geometryDescriptors = @[ geometryDescriptor ]; &#9;// Build the acceleration structure. &#9;id &lt;MTLAccelerationStructure&gt; accelerationStructure = [self newAccelerationStructureWithDescriptor:accelDescriptor]; &#9;// Add the acceleration structure to the array of primitive acceleration structures. &#9;[_primitiveAccelerationStructures addObject:accelerationStructure]; &#9;} In Swift, I am trying: for i in 0..<( scene.nodes.count ) &#9;{ &#9;let aMesh = scene.nodes[i] &#9;let geometryDescriptor: MTLAccelerationStructureGeometryDescriptor = aMesh.getGeometryDescriptor() &#9;// Assign each piece of geometry a consecutive slot in the intersection function table             geometryDescriptor.intersectionFunctionTableOffset = i &#9;// Create a primitive acceleration structure descriptor to contain the single piece of acceleration structure geometry &#9;var accelDescriptor: MTLPrimitiveAccelerationStructureDescriptor = MTLPrimitiveAccelerationStructureDescriptor() &#9;accelDescriptor.geometryDescriptors.append( geometryDescriptor ) &#9;// Build the acceleration structure. &#9;// To follow... &#9;// Add the acceleration structure to the array of primitive acceleration structures. &#9; // To follow... &#9;} The compiler flags appending the geometryDescriptor with "Cannot use mutating member on immutable value: 'accelDescriptor is immutable'". I have tried a couple of compiler suggested ideas to unwrap the accelDescriptor.geometryDescriptors, but end up with a nil value in the geometryDescriptors array. It may be naive to simply append the geometryDescriptor, but I would appreciate any suggestions to fill in the accelDescriptor. In the larger picture, it would be great to have a Swift Project sample to use as a starting point. The concepts spelled out in the video and Objective C project are very compelling! Thanks so much - John Lobe
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Jun ’20