Chromium源码由浅入深（一）

工作中需要对Chromium源码、尤其是源码中图形部分进行深入研究，所以借此机会边学习边写文章，分享一下我的实时学习研究Chromium源码的由浅入深的过程。

闲言少叙，书归正传。

通过命令行启动Chrome浏览器，命令及结果如下：

$ google-chrome-stable 
MESA-INTEL: warning: Performance support disabled, consider sysctl dev.i915.perf_stream_paranoid=0
 

在浏览器地址栏中输入“chrome://gpu”，得到以下结果：

第一步工作就是要找到如上所示的信息在Chromium源码中的具体位置。

经过查找定位，以上信息对应的代码在Chromium源码目录的content/browser/resources/gpu/info_view.js中，如下所示：

appendFeatureInfo_(
      featureInfo, featureStatusList, problemsDiv, problemsList, workaroundsDiv,
      workaroundsList) {
    // Feature map
    const featureLabelMap = {
      '2d_canvas': 'Canvas',
      'gpu_compositing': 'Compositing',
      'webgl': 'WebGL',
      'multisampling': 'WebGL multisampling',
      'texture_sharing': 'Texture Sharing',
      'video_decode': 'Video Decode',
      'rasterization': 'Rasterization',
      'opengl': 'OpenGL',
      'metal': 'Metal',
      'vulkan': 'Vulkan',
      'multiple_raster_threads': 'Multiple Raster Threads',
      'native_gpu_memory_buffers': 'Native GpuMemoryBuffers',
      'protected_video_decode': 'Hardware Protected Video Decode',
      'surface_control': 'Surface Control',
      'vpx_decode': 'VPx Video Decode',
      'webgl2': 'WebGL2',
      'canvas_oop_rasterization': 'Canvas out-of-process rasterization',
      'raw_draw': 'Raw Draw',
      'video_encode': 'Video Encode',
      'direct_rendering_display_compositor':
          'Direct Rendering Display Compositor',
      'webgpu': 'WebGPU',
    };
 
    const statusMap = {
      'disabled_software': {
        'label': 'Software only. Hardware acceleration disabled',
        'class': 'feature-yellow',
      },
      'disabled_off': {'label': 'Disabled', 'class': 'feature-red'},
      'disabled_off_ok': {'label': 'Disabled', 'class': 'feature-yellow'},
      'unavailable_software': {
        'label': 'Software only, hardware acceleration unavailable',
        'class': 'feature-yellow',
      },
      'unavailable_off': {'label': 'Unavailable', 'class': 'feature-red'},
      'unavailable_off_ok': {'label': 'Unavailable', 'class': 'feature-yellow'},
      'enabled_readback': {
        'label': 'Hardware accelerated but at reduced performance',
        'class': 'feature-yellow',
      },
      'enabled_force': {
        'label': 'Hardware accelerated on all pages',
        'class': 'feature-green',
      },
      'enabled': {'label': 'Hardware accelerated', 'class': 'feature-green'},
      'enabled_on': {'label': 'Enabled', 'class': 'feature-green'},
      'enabled_force_on': {'label': 'Force enabled', 'class': 'feature-green'},
    };
 
    // feature status list
    featureStatusList.textContent = '';
    for (const featureName in featureInfo.featureStatus) {
      const featureStatus = featureInfo.featureStatus[featureName];
      const featureEl = document.createElement('li');
 
      const nameEl = document.createElement('span');
      if (!featureLabelMap[featureName]) {
        console.info('Missing featureLabel for', featureName);
      }
      nameEl.textContent = featureLabelMap[featureName] + ': ';
      featureEl.appendChild(nameEl);
 
      const statusEl = document.createElement('span');
      const statusInfo = statusMap[featureStatus];
      if (!statusInfo) {
        console.info('Missing status for ', featureStatus);
        statusEl.textContent = 'Unknown';
        statusEl.className = 'feature-red';
      } else {
        statusEl.textContent = statusInfo['label'];
        statusEl.className = statusInfo['class'];
      }
      featureEl.appendChild(statusEl);
 
      featureStatusList.appendChild(featureEl);
    }
 
    // problems list
    if (featureInfo.problems.length) {
      problemsDiv.hidden = false;
      problemsList.textContent = '';
      for (const problem of featureInfo.problems) {
        const problemEl = this.createProblemEl_(problem);
        problemsList.appendChild(problemEl);
      }
    } else {
      problemsDiv.hidden = true;
    }
 
    // driver bug workarounds list
    if (featureInfo.workarounds.length) {
      workaroundsDiv.hidden = false;
      workaroundsList.textContent = '';
      for (const workaround of featureInfo.workarounds) {
        const workaroundEl = document.createElement('li');
        workaroundEl.textContent = workaround;
        workaroundsList.appendChild(workaroundEl);
      }
    } else {
      workaroundsDiv.hidden = true;
    }
  }

可以看到，上边网页中显示的内容大部分都能对应到代码中的featureLabelMap和statusMap中。比如：网页中“Graphics Feature Status”下的“Canvas: Hardware accelerated”、“Compositing: Hardware accelerated”、“OpenGL: Enabled”、“Video Decode: Hardware accelerated”、“Video Encode: Software only. Hardware acceleration disabled”、“Vulkan: Disabled”、“WebGPU: Disabled”等等。

那么appendFeatureInfo_函数也就不难理解了。一段一段来看。

首先来看以下代码片段：

 // feature status list
    featureStatusList.textContent = '';
    for (const featureName in featureInfo.featureStatus) {
      const featureStatus = featureInfo.featureStatus[featureName];
      const featureEl = document.createElement('li');
 
      const nameEl = document.createElement('span');
      if (!featureLabelMap[featureName]) {
        console.info('Missing featureLabel for', featureName);
      }
      nameEl.textContent = featureLabelMap[featureName] + ': ';
      featureEl.appendChild(nameEl);
 
      const statusEl = document.createElement('span');
      const statusInfo = statusMap[featureStatus];
      if (!statusInfo) {
        console.info('Missing status for ', featureStatus);
        statusEl.textContent = 'Unknown';
        statusEl.className = 'feature-red';
      } else {
        statusEl.textContent = statusInfo['label'];
        statusEl.className = statusInfo['class'];
      }
      featureEl.appendChild(statusEl);
 
      featureStatusList.appendChild(featureEl);
    }

代码注释说得很清楚，这段是“feature status list”，从这里就可以看出来是对应Chrome网页中的“Graphics Feature Status”。

featureInfo是调用appendFeatureInfo_函数时传下来的，暂时不管其实际内容。循环处理featureInfo.featureStatus中的每一项。

先要获得每一项的featureStatus；然后调用document.createElement("li")和document.createElement("span")分别创建“li”标签和“span标签”节点（笔者对于JavaScript不熟，如有错误请指正）；再往下根据每个项的featureLabelMap[featureName]和statusMap[featureStatus]向网页中添加该项的名称和状态，状态还要带上颜色。就是网页中的那些项。

接下来是以下代码片段：

    // problems list
    if (featureInfo.problems.length) {
      problemsDiv.hidden = false;
      problemsList.textContent = '';
      for (const problem of featureInfo.problems) {
        const problemEl = this.createProblemEl_(problem);
        problemsList.appendChild(problemEl);
      }
    } else {
      problemsDiv.hidden = true;
    }

代码注释说得也很明白，这段是“problems list”。

featureInfo是调用appendFeatureInfo_函数时传下来的，暂时不管其实际内容。循环处理featureInfo.problems中的每一项。

再往下是以下代码片段：

    // driver bug workarounds list
    if (featureInfo.workarounds.length) {
      workaroundsDiv.hidden = false;
      workaroundsList.textContent = '';
      for (const workaround of featureInfo.workarounds) {
        const workaroundEl = document.createElement('li');
        workaroundEl.textContent = workaround;
        workaroundsList.appendChild(workaroundEl);
      }
    } else {
      workaroundsDiv.hidden = true;
    }

代码注释说得也很明白，这段是“driver bug workaround list”，从这里就可以看出来是对应Chrome网页中的“Driver Bug Workarounds”。

featureInfo是调用appendFeatureInfo_函数时传下来的，暂时不管其实际内容。循环处理featureInfo.workaroundsList中的每一项。

至此，网页中的gpu相关信息在代码中的定位以及appendFeatureInfo_函数就解析完了。

预知后事如何，且看下回分解。