test: Shrink the example triangle to demonstrate the rendering comparison

.github/workflows/ci.yml

@@ -59,7 +59,8 @@ jobs:
           echo "- Shared: ${{ steps.filter.outputs.shared == 'true' && '✅' || '❌' }}" >> $GITHUB_STEP_SUMMARY
 
   # Note the build jobs are split into two jobs for vc6 and win32 because the replay checks
-  # only require the vc6 build and compiling vc6 is much faster than win32
+  # only require the vc6 build and compiling vc6 is much faster than win32,
+  # and the rendering checks only require the win32 build.
   build-generals-vc6:
     name: Build Generals${{ matrix.preset && '' }}
     needs: detect-changes
@@ -237,3 +238,25 @@ jobs:
       userdata: "GeneralsReplays/GeneralsZH/1.04"
       preset: ${{ matrix.preset }}
     secrets: inherit
+
+  renderingcheck-generals:
+    name: Rendering Check Generals
+    needs: [detect-changes, build-generals-win32]
+    if: ${{ github.event_name == 'workflow_dispatch' || needs.detect-changes.outputs.generals == 'true' || needs.detect-changes.outputs.shared == 'true' }}
+    permissions:
+      contents: read
+      actions: read
+    uses: ./.github/workflows/reusable-check-rendering.yml
+    with:
+      game: "Generals"
+
+  renderingcheck-generalsmd:
+    name: Rendering Check GeneralsMD
+    needs: [detect-changes, build-generalsmd-win32]
+    if: ${{ github.event_name == 'workflow_dispatch' || needs.detect-changes.outputs.generalsmd == 'true' || needs.detect-changes.outputs.shared == 'true' }}
+    permissions:
+      contents: read
+      actions: read
+    uses: ./.github/workflows/reusable-check-rendering.yml
+    with:
+      game: "GeneralsMD"

.github/workflows/reusable-build-toolchain.yml

@@ -175,12 +175,27 @@ jobs:
 
       # The benchmarks are only built, because running them takes too long here.
       # Verbose prints the Google Test output, which lists the test cases of each executable.
+      # The rendering tests run in the rendering check of ci.yml instead.
       - name: Test ${{ inputs.game }} with CTest Using ${{ inputs.preset }}${{ inputs.tools && '+t' || '' }}${{ inputs.extras && '+e' || '' }} Preset
         if: ${{ inputs.tests }}
         shell: pwsh
+        env:
+          GTEST_FILTER: -RenderingTest.*
         run: |
           ctest --preset ${{ inputs.preset }} --verbose
 
+      # Keep this package separate from the game release artifacts. Only the plain
+      # win32 Release build is needed for the rendering check in ci.yml, whose runner has the CRT.
+      - name: Upload Rendering Test Executable
+        if: ${{ inputs.tests && inputs.preset == 'win32' }}
+        uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f # v7.0.0
+        with:
+          name: ${{ inputs.game }}-win32-rendering-tests
+          path: build/${{ inputs.preset }}/Tests/Google/Release/${{ inputs.game == 'Generals' && 'g' || 'z' }}_googletest.exe
+          # Kept longer on main, where pull requests download it to compare their rendering with.
+          retention-days: ${{ github.ref == 'refs/heads/main' && 90 || 7 }}
+          if-no-files-found: error
+
       - name: Collect ${{ inputs.game }} ${{ inputs.preset }}${{ inputs.tools && '+t' || '' }}${{ inputs.extras && '+e' || '' }} Artifact
         shell: pwsh
         run: |

.github/workflows/reusable-check-rendering.yml

@@ -0,0 +1,191 @@
+name: Check Rendering
+
+# WARNING: Do not declare permissions in this reusable workflow.
+# Declare the required permissions in each calling job:
+#   contents: read - required for rendering checks.
+#   actions: read - required to download the rendering tests of the base commit.
+
+on:
+  workflow_call:
+    inputs:
+      game:
+        required: true
+        type: string
+        description: "Game to check (Generals, GeneralsMD)"
+
+jobs:
+  rendering:
+    name: DXVK and lavapipe
+    runs-on: windows-2022
+    timeout-minutes: 15
+    env:
+      GAME: ${{ inputs.game }}
+      TEST_NAME: ${{ inputs.game == 'Generals' && 'g_googletest' || 'z_googletest' }}
+      # Google Test reads its flags from these as well.
+      GTEST_FILTER: RenderingTest.*
+      GTEST_FAIL_IF_NO_TEST_SELECTED: 1
+      GTEST_OUTPUT: xml:results.xml
+      # The pinned Mesa version decides the rendering, not the runner image.
+      DXVK_VERSION: 2.6.2
+      DXVK_SHA256: 17761876556afd55736cb895d184f5a1c55d43350f1b1e3b129f8d28706d7992
+      MESA_VERSION: 26.2.4
+      MESA_SHA256: 351fc8c8b695878ffb3eaa044b3ead08672a48b1a045e3c3e3975811df0f6695
+      VULKAN_RUNTIME_VERSION: 1.4.363.0
+      VULKAN_RUNTIME_SHA256: a25a927aa8b9f0371048f1861cf88ac3b9bc9b1fb332c42d897c8ab32695769a
+    steps:
+      - name: Checkout Code
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+      - name: Download MSVC Rendering Tests
+        uses: actions/download-artifact@70fc10c6e5e1ce46ad2ea6f2b72d43f7d47b13c3 # v8.0.0
+        with:
+          name: ${{ inputs.game }}-win32-rendering-tests
+          path: build/rendering-tests
+
+      - name: Install DXVK and Lavapipe
+        run: |
+          $PSNativeCommandUseErrorActionPreference = $true
+          function Get-Checked($url, $out, $sha) {
+            curl.exe --fail --location --retry 3 --output $out $url
+            if ((Get-FileHash $out SHA256).Hash -ne $sha) { throw "SHA256 mismatch for $url" }
+          }
+          $dxvk = "dxvk-$env:DXVK_VERSION"
+          Get-Checked "https://github.com/doitsujin/dxvk/releases/download/v$env:DXVK_VERSION/$dxvk.tar.gz" build/dxvk.tar.gz $env:DXVK_SHA256
+          Get-Checked "https://github.com/pal1000/mesa-dist-win/releases/download/$env:MESA_VERSION/mesa3d-$env:MESA_VERSION-release-msvc.7z" build/mesa.7z $env:MESA_SHA256
+          Get-Checked "https://sdk.lunarg.com/sdk/download/$env:VULKAN_RUNTIME_VERSION/windows/vulkan-runtime-components.zip" build/vulkan.zip $env:VULKAN_RUNTIME_SHA256
+          # The 32-bit DLLs that go beside each test exe.
+          New-Item -ItemType Directory build/runtime | Out-Null
+          tar -C build/runtime -xf build/dxvk.tar.gz --strip-components=2 "$dxvk/x32/d3d8.dll" "$dxvk/x32/d3d9.dll"
+          7z e build/vulkan.zip -obuild/runtime "VulkanRT-X64-$env:VULKAN_RUNTIME_VERSION-Components/x86/vulkan-1.dll"
+          7z e build/mesa.7z -obuild/lavapipe x86/vulkan_lvp.dll x86/lvp_icd.x86.json
+          # The runner is elevated, so the Vulkan loader ignores VK_DRIVER_FILES. Register 32-bit lavapipe instead.
+          reg add HKLM\SOFTWARE\WOW6432Node\Khronos\Vulkan\Drivers /v "$PWD\build\lavapipe\lvp_icd.x86.json" /t REG_DWORD /d 0 /f
+
+      - name: Run Rendering Google Tests
+        working-directory: build/rendering-tests
+        timeout-minutes: 5
+        run: |
+          Copy-Item ../runtime/* .
+          & "./$env:TEST_NAME.exe"
+
+      - name: Download Base Rendering Tests
+        id: base
+        if: always()
+        env:
+          GH_TOKEN: ${{ github.token }}
+          PUSH_BEFORE: ${{ github.event.before }}
+          PR_BASE: ${{ github.event.pull_request.base.sha }}
+          PR_HEAD: ${{ github.event.pull_request.head.sha }}
+          PR_HEAD_OWNER: ${{ github.event.pull_request.head.repo.owner.login }}
+        run: |
+          # Compare with the commit this change is based on: the previous main commit for a push,
+          # otherwise the merge base with main. Its GenCI run already built the rendering tests.
+          # A failed gh api call prints the error to stdout, so each call checks its exit code.
+          $repo = "repos/$env:GITHUB_REPOSITORY"
+          $base = switch ($env:GITHUB_EVENT_NAME) {
+            'push' { $env:PUSH_BEFORE }
+            'pull_request' { gh api "$repo/compare/${env:PR_BASE}...${env:PR_HEAD_OWNER}:${env:PR_HEAD}" --jq .merge_base_commit.sha }
+            default { gh api "$repo/compare/main...$env:GITHUB_SHA" --jq .merge_base_commit.sha }
+          }
+          if ($LASTEXITCODE) { $base = $null }
+          # A commit has no package when it was pushed together with later commits, or when its run
+          # skipped this game's build because nothing it builds from changed. The nearest ancestor
+          # with a package then renders the same.
+          $commits = @()
+          if ($base) {
+            $commits = gh api "$repo/commits?sha=$base&per_page=20" --jq '.[].sha'
+            if ($LASTEXITCODE) { $commits = @() }
+          }
+          foreach ($commit in $commits) {
+            $runs = gh api "$repo/actions/runs?head_sha=$commit" --jq ".workflow_runs[] | select(.id != $env:GITHUB_RUN_ID) | .id"
+            if ($LASTEXITCODE) { continue }
+            foreach ($run in $runs) {
+              gh run download $run --repo $env:GITHUB_REPOSITORY --name "${env:GAME}-win32-rendering-tests" --dir build/rendering-tests-base
+              if ($LASTEXITCODE -eq 0) {
+                "Using the rendering tests of run $run for commit $commit (base commit $base)"
+                "sha=$commit" >> $env:GITHUB_OUTPUT
+                exit 0
+              }
+              Remove-Item -Recurse -Force -ErrorAction Ignore build/rendering-tests-base
+            }
+          }
+          "::notice title=Rendering::No rendering tests found for base commit $($base ?? 'unknown'), so the images are not compared"
+          exit 0
+
+      - name: Run Base Rendering Google Tests
+        if: ${{ always() && steps.base.outputs.sha }}
+        working-directory: build/rendering-tests-base
+        timeout-minutes: 5
+        run: |
+          Copy-Item ../runtime/* .
+          & "./$env:TEST_NAME.exe"
+          if ($LASTEXITCODE) { "::warning title=Rendering::The base rendering tests failed, so only the images they wrote are compared" }
+          exit 0
+
+      - name: Compare Rendering with Base
+        id: compare
+        if: always()
+        env:
+          BASE_SHA: ${{ steps.base.outputs.sha }}
+        run: |
+          $since = if ($env:BASE_SHA) { "since base $($env:BASE_SHA.Substring(0, 10))" } else { '(no base found)' }
+          function Get-Image($path) {
+            if (Test-Path $path) { "<img src=`"data:image/png;base64,$([Convert]::ToBase64String([IO.File]::ReadAllBytes((Resolve-Path $path))))`">" }
+          }
+          # The same PNG encoder wrote both images, so equal pixels give equal files.
+          $images = foreach ($name in (Get-ChildItem build/rendering-tests*/*.png).Name | Sort-Object -Unique) {
+            $old = Get-Image build/rendering-tests-base/$name
+            $new = Get-Image build/rendering-tests/$name
+            $state = if (!$old) { 'new' } elseif (!$new) { 'removed' } elseif ($old -eq $new) { 'unchanged' } else { 'changed' }
+            [pscustomobject]@{ Name = $name; State = $state; Old = $old; New = $new }
+          }
+          $changes = ($images | Where-Object State -in 'changed', 'removed' | ForEach-Object { "$($_.Name) $($_.State)" }) -join ', '
+          "changes=$changes" >> $env:GITHUB_OUTPUT
+          "message=$(if ($changes) { $changes } else { 'No changes' }) $since" >> $env:GITHUB_OUTPUT
+          "### $env:GAME Rendering`n`n$(($images | Group-Object State | ForEach-Object { "$($_.Count) $($_.Name)" }) -join ', ') $since.`n" >> $env:GITHUB_STEP_SUMMARY
+          # One page with the images inline, so the browser opens the artifact without unzipping. The difference
+          # blends the new image over the base and brightens the result, so only changed pixels show.
+          $rows = foreach ($image in $images | Sort-Object State, Name) {
+            $diff = if ($image.State -eq 'changed') { "<div class=diff>$($image.Old)$($image.New)</div>" }
+            "<tr><th>$($image.Name)<br>$($image.State)</th><td>$($image.Old)</td><td>$($image.New)</td><td>$diff</td></tr>"
+          }
+          @"
+          <!doctype html>
+          <meta charset="utf-8">
+          <title>$env:GAME rendering $since</title>
+          <style>
+          body { font-family: sans-serif } th, td { padding: 8px; text-align: left; vertical-align: top }
+          .diff { position: relative; filter: brightness(1000) } .diff img + img { position: absolute; top: 0; left: 0; mix-blend-mode: difference }
+          </style>
+          <h1>$env:GAME rendering $since</h1>
+          <table>
+          <tr><th></th><th>Base</th><th>This commit</th><th>Difference</th></tr>
+          $($rows -join "`n")
+          </table>
+          "@ | Set-Content "build/$env:GAME-rendering-report.html"
+
+      # A single file is uploaded unzipped, so its link opens it in the browser.
+      - name: Upload Rendering Report
+        id: report
+        if: always()
+        uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f # v7.0.0
+        with:
+          path: build/${{ inputs.game }}-rendering-report.html
+          archive: false
+          retention-days: 7
+          if-no-files-found: warn
+
+      # Comes after the upload, so the message that a failed check opens with links to the report.
+      # Changes fail pull requests, so reviewers check in the report whether they are intended.
+      # On main they are warnings, because main becomes the base of later changes.
+      - name: Check Rendering Changes
+        if: always()
+        env:
+          CHANGES: ${{ steps.compare.outputs.changes }}
+          MESSAGE: ${{ steps.compare.outputs.message }}
+          REPORT_URL: ${{ steps.report.outputs.artifact-url }}
+        run: |
+          "[Open the $env:GAME rendering report]($env:REPORT_URL)" >> $env:GITHUB_STEP_SUMMARY
+          $level = if (!$env:CHANGES) { 'notice' } elseif ($env:GITHUB_EVENT_NAME -eq 'pull_request') { 'error' } else { 'warning' }
+          "::$level title=$env:GAME rendering::$env:MESSAGE. Report: $env:REPORT_URL"
+          if ($level -eq 'error') { exit 1 }

Tests/Google/Core/CMakeLists.txt

@@ -15,6 +15,10 @@ set(COREI_GOOGLETEST_SRC
     Libraries/WWVegas/WWMath/WWMathKeys.h
     Libraries/WWVegas/WWMath/WWMathTest.cpp
     Libraries/WWVegas/WWMath/WWMathTestCase.h
+    Rendering/EXAMPLE_TEMPORARY_ClearTest.cpp
+    Rendering/EXAMPLE_TEMPORARY_TriangleTest.cpp
+    Rendering/RenderingTestFixture.cpp
+    Rendering/RenderingTestFixture.h
 )
 
 add_library(corei_googletest INTERFACE)
@@ -26,6 +30,7 @@ target_link_libraries(corei_googletest INTERFACE
     depsi_googletest
     GTest::gtest
     imm32
+    stb
     vfw32
     winmm
 )

Tests/Google/Core/Rendering/EXAMPLE_TEMPORARY_ClearTest.cpp

@@ -0,0 +1,29 @@
+/*
+**	Command & Conquer Generals Zero Hour(tm)
+**	Copyright 2026 TheSuperHackers
+**
+**	This program is free software: you can redistribute it and/or modify
+**	it under the terms of the GNU General Public License as published by
+**	the Free Software Foundation, either version 3 of the License, or
+**	(at your option) any later version.
+**
+**	This program is distributed in the hope that it will be useful,
+**	but WITHOUT ANY WARRANTY; without even the implied warranty of
+**	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+**	GNU General Public License for more details.
+**
+**	You should have received a copy of the GNU General Public License
+**	along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "RenderingTestFixture.h"
+
+// Clearing the render target fills it with the clear color from corner to corner.
+TEST_F(RenderingTest, Clear)
+{
+	const DWORD color = 0x102030;
+	clear(color);
+	capture("clear.png");
+	EXPECT_EQ(pixel(0, 0), color);
+	EXPECT_EQ(pixel(Width - 1, Height - 1), color);
+}

Tests/Google/Core/Rendering/EXAMPLE_TEMPORARY_TriangleTest.cpp

@@ -0,0 +1,35 @@
+/*
+**	Command & Conquer Generals Zero Hour(tm)
+**	Copyright 2026 TheSuperHackers
+**
+**	This program is free software: you can redistribute it and/or modify
+**	it under the terms of the GNU General Public License as published by
+**	the Free Software Foundation, either version 3 of the License, or
+**	(at your option) any later version.
+**
+**	This program is distributed in the hope that it will be useful,
+**	but WITHOUT ANY WARRANTY; without even the implied warranty of
+**	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+**	GNU General Public License for more details.
+**
+**	You should have received a copy of the GNU General Public License
+**	along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "RenderingTestFixture.h"
+
+// A triangle with a red, a green and a blue corner blends the corner colors across its area.
+TEST_F(RenderingTest, Triangle)
+{
+	const DWORD background = 0x102030;
+	clear(background);
+	drawTriangles({
+		{128.0f, 80.0f, 0xff0000},
+		{192.0f, 200.0f, 0x00ff00},
+		{64.0f, 200.0f, 0x0000ff},
+	});
+	capture("triangle.png");
+	// GPUs round the blended colors differently, so the exact colors are left to the image comparison of CI.
+	EXPECT_EQ(pixel(8, 8), background);
+	EXPECT_NE(pixel(128, 160), background);
+}