tools/android/webgpu/src/androidTest/java/androidx/webgpu/MultisampleStateTest.kt

/*
 * Copyright 2025 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package androidx.webgpu

import androidx.test.ext.junit.runners.AndroidJUnit4
import androidx.test.filters.MediumTest
import androidx.webgpu.WebGpuTestConstants.EMULATOR_TESTS_MIN_API_LEVEL
import androidx.webgpu.helper.createWebGpu
import androidx.webgpu.helper.WebGpu
import java.util.concurrent.Executors
import kotlinx.coroutines.CoroutineDispatcher
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.ExecutorCoroutineDispatcher
import kotlinx.coroutines.asCoroutineDispatcher
import kotlinx.coroutines.cancel
import kotlinx.coroutines.launch
import kotlinx.coroutines.runBlocking
import org.junit.After
import org.junit.Assert.assertEquals
import org.junit.Before
import org.junit.Rule
import org.junit.Test
import org.junit.runner.RunWith

@RunWith(AndroidJUnit4::class)
@MediumTest
class MultisampleStateTest {
  companion object {
    private const val MSAA_COUNT = 4
    private const val TEXTURE_FORMAT = TextureFormat.RGBA8Unorm
    private const val WIDTH = 4
    private const val HEIGHT = 4
    private const val BYTES_PER_ROW = 256
  }

  private val dispatcher: CoroutineDispatcher = Executors.newSingleThreadExecutor { runnable ->
    Thread(runnable, "Test-WebGPU-Thread")
  }.asCoroutineDispatcher()
  private val testScope = CoroutineScope(dispatcher)
  private lateinit var device: GPUDevice
  private lateinit var webGpu: WebGpu
  @get:Rule val apiSkipRule = ApiLevelSkipRule()

  @Before
  fun setup(): Unit = runBlocking {
    webGpu = createWebGpu(dispatcher)
    device = webGpu.device
    testScope.launch {
      webGpu.processEventsLoop()
    }
  }

  @After
  fun teardown() {
    if (::webGpu.isInitialized) {
      webGpu.close()
    }
    testScope.cancel()
    (dispatcher as? ExecutorCoroutineDispatcher)?.close()
  }

  /**
   * Helper function to run the MSAA test with a specific sample mask.
   * returns the Red channel value of the first pixel (0-255).
   */
  private suspend fun executeMsaaTest(multiSampleState: GPUMultisampleState): Int {
    // 1. Create Textures
    val msaaTexture = device.createTexture(
      GPUTextureDescriptor(
        size = GPUExtent3D(WIDTH, HEIGHT, 1),
        format = TEXTURE_FORMAT,
        usage = TextureUsage.RenderAttachment,
        sampleCount = MSAA_COUNT
      )
    )

    val resolveTexture = device.createTexture(
      GPUTextureDescriptor(
        size = GPUExtent3D(WIDTH, HEIGHT, 1),
        format = TEXTURE_FORMAT,
        usage = TextureUsage.RenderAttachment or TextureUsage.CopySrc,
        sampleCount = 1
      )
    )

    // 2. Create Output Buffer
    val outputBufferSize = (HEIGHT * BYTES_PER_ROW).toLong()
    val outputBuffer = device.createBuffer(
      GPUBufferDescriptor(
        size = outputBufferSize,
        usage = BufferUsage.CopyDst or BufferUsage.MapRead
      )
    )

    // 3. Create Pipeline with the specific Mask
    val shaderModule = device.createShaderModule(
      GPUShaderModuleDescriptor(
        shaderSourceWGSL = GPUShaderSourceWGSL(
          code = """
                        @vertex fn vs(@builtin(vertex_index) vi: u32) -> @builtin(position) vec4f {
                            var pos = array<vec2f, 3>(
                                vec2f(-1.0, -1.0), vec2f(3.0, -1.0), vec2f(-1.0, 3.0)
                            );
                            return vec4f(pos[vi], 0.0, 1.0);
                        }
                        @fragment fn fs() -> @location(0) vec4f {
                            return vec4f(1.0, 1.0, 1.0, 1.0); // Output White
                        }
                    """
        )
      )
    )

    val pipeline = device.createRenderPipeline(
      GPURenderPipelineDescriptor(
        vertex = GPUVertexState(module = shaderModule, entryPoint = "vs"),
        fragment = GPUFragmentState(
          module = shaderModule,
          entryPoint = "fs",
          targets = arrayOf(GPUColorTargetState(format = TEXTURE_FORMAT))
        ),
        primitive = GPUPrimitiveState(topology = PrimitiveTopology.TriangleList),
        multisample = multiSampleState
      )
    )

    // 4. Render Pass
    val encoder = device.createCommandEncoder()
    val pass = encoder.beginRenderPass(
      GPURenderPassDescriptor(
        colorAttachments = arrayOf(
          GPURenderPassColorAttachment(
            view = msaaTexture.createView(),
            resolveTarget = resolveTexture.createView(),
            loadOp = LoadOp.Clear,
            clearValue = GPUColor(0.0, 0.0, 0.0, 1.0), // Clear to Black
            storeOp = StoreOp.Discard
          )
        )
      )
    )
    pass.setPipeline(pipeline)
    pass.draw(3)
    pass.end()

    // 5. Copy & Resolve
    encoder.copyTextureToBuffer(
      source = GPUTexelCopyTextureInfo(texture = resolveTexture),
      destination = GPUTexelCopyBufferInfo(
        buffer = outputBuffer,
        layout = GPUTexelCopyBufferLayout(offset = 0, bytesPerRow = BYTES_PER_ROW)
      ),
      copySize = GPUExtent3D(WIDTH, HEIGHT, 1)
    )

    device.queue.submit(arrayOf(encoder.finish()))

    device.queue.onSubmittedWorkDone()
    outputBuffer.mapAndAwait(MapMode.Read, 0, outputBufferSize)

    // 6. Read Result
    val data = outputBuffer.getConstMappedRange()
    val r = data.get(0).toInt() and 0xFF

    outputBuffer.unmap()
    outputBuffer.destroy()
    resolveTexture.destroy()
    msaaTexture.destroy()

    return r
  }

  @Test
  @ApiRequirement(minApi = EMULATOR_TESTS_MIN_API_LEVEL, onlySkipOnEmulator = true)
  fun verifyDefaultMaskEnablesAllSamplesInMSAARender() = runBlocking {
    val unused = webGpu.execute {
      // Default mask (0xFFFFFFFF or -1) should allow drawing.
      // We draw White on Black background -> Expect White (255).
      val actualValue = executeMsaaTest(
        GPUMultisampleState(
          count = MSAA_COUNT,
        )
      )
      assertEquals("Should be White (255)", 255, actualValue)
    }
  }

  @Test
  fun verifyZeroMaskDisablesUpdates() = runBlocking {
    val unused = webGpu.execute {
      // Zero mask (0x0) should block all samples from being updated.
      // We draw White on Black background -> Expect Black (0) because the draw was masked out.
      val actualValue = executeMsaaTest(
        GPUMultisampleState(
          count = MSAA_COUNT,
          mask = 0
        )
      )
      assertEquals("Should be Black (0) because mask prevented write", 0, actualValue)
    }
  }
}