RtxdiProgram.kt

src/jvmMain/kotlin/afield/graphics/render/lighting/RtxdiProgram.kt · 56 lines

package afield.graphics.render.lighting

import afield.graphics.shader.Introspection
import afield.graphics.shader.ShaderKind
import org.json.JSONObject
import java.io.File
import java.security.MessageDigest

Loads the optional RTXDI shaders, and refuses a binary whose interface disagrees with the host code written against it.

Field does not ship NVIDIA's sampling SDK and loads nothing from it at startup. Running tools/lighting/build_rtxdi.py --prepare clones the SDK and fetches a shader compiler into ignored build storage, and the build leaves a manifest under build/lighting-experiment/rtxdi-shaders/. load reads that manifest; with no manifest there it fails with the command to run.

What load then checks is the interface rather than the file. The manifest has to record the SDK commit this source was written against, the SPIR-V has to hash to what the manifest recorded, and the shader's own reflection has to still carry the workgroup size, the push-constant block's size and member offsets, the reservoir and offset array strides, and the surface and light struct layouts that the host side writes into. Shaders rebuilt from a different SDK revision therefore fail to load, instead of being handed the host's bytes at offsets that have moved.

A loaded program is passed to DirectLighting through enableRtxdi, which builds the pass and leaves the current one in place if that fails.

class RtxdiProgram private constructor(val manifest: JSONObject, internal val reflection: Introspection)

Optional compiled SDK shaders. Build with tools/lighting/build_rtxdi.py; no SDK is loaded at startup.

companion object

const val SDK_COMMIT = "f12037fa8e97ebc08e9e3edfd2de528ed1772a4b"

fun load(manifestFile: File = File("build/lighting-experiment/rtxdi-shaders/current.json")): RtxdiProgram

        fun load(manifestFile: File = File("build/lighting-experiment/rtxdi-shaders/current.json")): RtxdiProgram {
            require(manifestFile.isFile) { "Build the optional RTXDI shaders first: uv run python tools/lighting/build_rtxdi.py --prepare" }
            val manifest=JSONObject(manifestFile.readText())
            require(manifest.getInt("schema")==1 && manifest.getString("sdkCommit")==SDK_COMMIT)
            val binary=File(manifest.getString("spirv")).readBytes()
            val hash=MessageDigest.getInstance("SHA-256").digest(binary).joinToString("") { "%02x".format(it) }
            require(hash==manifest.getString("spirvSha256")) { "RTXDI SPIR-V checksum mismatch" }
            val info=Introspection.fromSpirv("Field RTXDI bridge",ShaderKind.COMPUTE_SHADER,binary)
            require(info.valid && info.fixedWorkgroupSize==listOf(8,8,1))
            require(info.pushConstants.single().size==112) { "RTXDI host/shader push ABI changed" }
            require(info.pushConstants.single().members.map { it.offset } ==
                listOf(0,8,16,24)+(32..108 step 4).toList()) { "RTXDI push member offsets changed" }
            require(info.ssbo.single { it.name=="reservoirs" }.members.single().arrayStride==24)
            require(info.ssbo.single { it.name=="offsets" }.members.single().arrayStride==8)
            for(name in listOf("SurfaceData","RAB_LightInfo")) {
                val type=info.structureTypes.single { it.name==name }
                require(type.size==80 && type.members.map { it.offset }==listOf(0,16,32,48,64)) { "RTXDI $name ABI changed" }
            }
            return RtxdiProgram(manifest,info)
        }
    }
}