Why MTLTexture with 2D Array doesn't work? - ios

Question

I'm trying to replicate splat map technique from Unity tutorial. They use Texture2DArray so I created MTLTexture with this type:
private func createTerrainTexture(_ bundle: Bundle) -> MTLTexture {
guard let device = MTLCreateSystemDefaultDevice() else {
fatalError()
}
let names = ["sand", "grass", "earth", "stone", "snow"]
let loader = MTKTextureLoader(device: device)
let array = names.map { name -> MTLTexture in
do {
return try loader.newTexture(name: name, scaleFactor: 1.0, bundle: bundle, options: nil)
} catch {
fatalError()
}
}
guard let queue = device.makeCommandQueue() else {
fatalError()
}
guard let commandBuffer = queue.makeCommandBuffer() else {
fatalError()
}
guard let encoder = commandBuffer.makeBlitCommandEncoder() else {
fatalError()
}
let descriptor = MTLTextureDescriptor()
descriptor.textureType = .type2DArray
descriptor.pixelFormat = array[0].pixelFormat
descriptor.width = array[0].width
descriptor.height = array[0].height
descriptor.mipmapLevelCount = array[0].mipmapLevelCount
descriptor.arrayLength = 5
guard let texture = device.makeTexture(descriptor: descriptor) else {
fatalError()
}
var slice = 0
array.forEach { item in
encoder.copy(from: item,
sourceSlice: 0,
sourceLevel: 0,
sourceOrigin: MTLOrigin(x: 0, y: 0, z: 0),
sourceSize: MTLSize(width: item.width, height: item.height, depth: 1),
to: texture,
destinationSlice: slice,
destinationLevel: 0,
destinationOrigin: MTLOrigin(x: 0, y: 0, z: 0))
slice += 1
}
encoder.endEncoding()
commandBuffer.commit()
commandBuffer.waitUntilCompleted()
return texture
}
Here is my fragment shader function:
fragment half4 terrainFragment(TerrainVertexOutput in [[stage_in]],
texture2d_array<float> terrainTexture [[texture(0)]])
{
constexpr sampler sampler2d(coord::normalized, filter::linear, address::repeat);
float2 uv = in.position.xz * 0.02;
float4 c1 = terrainTexture.sample(sampler2d, uv, 0);
return half4(c1);
}
Here is Unity shader from tutorial:
void surf (Input IN, inout SurfaceOutputStandard o) {
float2 uv = IN.worldPos.xz * 0.02;
fixed4 c = UNITY_SAMPLE_TEX2DARRAY(_MainTex, float3(uv, 0));
Albedo = c.rgb * _Color;
o.Metallic = _Metallic;
o.Smoothness = _Glossiness;
o.Alpha = c.a;
}
For some reason I'm getting wrong result when texture repeated in columns.
Result I want to have is:
Update.
Here is how texture looks like in GPU Frame Debugger:
When I copy mipmaps like this:
var slice = 0
array.forEach { item in
print(item.width, item.height, item.mipmapLevelCount)
for i in 0..<descriptor.mipmapLevelCount {
encoder.copy(from: item,
sourceSlice: 0,
sourceLevel: i,
sourceOrigin: MTLOrigin(x: 0, y: 0, z: 0),
sourceSize: MTLSize(width: item.width, height: item.height, depth: 1),
to: texture,
destinationSlice: slice,
destinationLevel: i,
destinationOrigin: MTLOrigin(x: 0, y: 0, z: 0))
}
slice += 1
}
I'm getting error:
-[MTLDebugBlitCommandEncoder validateCopyFromTexture:sourceSlice:sourceLevel:sourceOrigin:sourceSize:toTexture:destinationSlice:destinationLevel:destinationOrigin:options:]:254: failed assertion `(sourceOrigin.x + sourceSize.width)(512) must be <= width(256).'

Answer 1

Problem was in incorrect porting of fragment shader input variable. In original input worldPos was used, but I used float4 position [[position]] and according to Metal specification this means
Describes the window-relative coordinate (x, y, z, 1/w) values for the fragment.
So position was incorrect. Here is how correct fragment shader input looks like:
struct TerrainVertexOutput
{
float4 position [[position]];
float3 p;
};
And vertex function:
vertex TerrainVertexOutput terrainVertex(TerrainVertexInput in [[stage_in]],
constant SCNSceneBuffer& scn_frame [[buffer(0)]],
constant MyNodeBuffer& scn_node [[buffer(1)]])
{
TerrainVertexOutput v;
v.position = scn_node.modelViewProjectionTransform * float4(in.position, 1.0);
v.p = (scn_node.modelTransform * float4(in.position, 1.0)).xyz;
return v;
}