Android 12(S) 图像显示系统 – drm_hwcomposer 简析(下)
- 2022 年 7 月 6 日
- 筆記
- Android 图形图像, Android图形图像
必读:
Android 12(S) 图像显示系统 – 开篇
合成方式
合成类型的定义:/hardware/interfaces/graphics/composer/2.1/IComposerClient.hal
/** Possible composition types for a given layer. */
/** 建议去看源码中的注释,可以理解每一个type的含义 */
enum Composition : int32_t {
INVALID = 0,
CLIENT = 1,
DEVICE = 2,
SOLID_COLOR = 3,
CURSOR = 4,
SIDEBAND = 5,
};
后端的设计逻辑
有三个类定义
1. Backend == 一个后端的实现,注册为”generic”,主要是定义了ValidateDisplay方法,这个方法用来设置可见的HwcLayer应该采用什么合成方式
2. BackendClient == 一个后端的实现,注册为”client”,主要是定义了ValidateDisplay方法,它把所有HwcLayer都设置成立Client合成方式
3. BackendManager == 后端的管理器,用来根据Device name从已注册的backend列表中选择一个,设置给HwcDisplay;GetBackendByName就是通过Device name来从available_backends_中选择一个匹配的Backend构造函数来构建后端对象。
HWC 中如何为每一个Layer选择合成方式
[drm-hwcomposer/hwc2_device/HwcDisplay.cpp]
HWC2::Error HwcDisplay::ValidateDisplay(uint32_t *num_types,
uint32_t *num_requests) {
if (IsInHeadlessMode()) {
*num_types = *num_requests = 0;
return HWC2::Error::None;
}
return backend_->ValidateDisplay(this, num_types, num_requests); //调用backend的方法
}
去调用到后端的具体validate方法,我的平台就是走到Backend::ValidateDisplay
[drm-hwcomposer/backend/Backend.cpp]
HWC2::Error Backend::ValidateDisplay(HwcDisplay *display, uint32_t *num_types,
uint32_t *num_requests) {
*num_types = 0;
*num_requests = 0;
auto layers = display->GetOrderLayersByZPos(); // 按Z-order顺序排列的HwcLayer的集合
int client_start = -1; // layers中,需要Client合成的layer的起始位置
size_t client_size = 0; // layers中,需要Client合成的layer的个数
if (display->ProcessClientFlatteningState(layers.size() <= 1)) {
display->total_stats().frames_flattened_++;
client_start = 0;
client_size = layers.size();
//设置合成类型,client_start到client_start+client_size之间的设置为Client,其它的设置为Device
MarkValidated(layers, client_start, client_size);
} else {
std::tie(client_start, client_size) = GetClientLayers(display, layers);// 刷选哪些layer需要Client合成
//设置合成类型,client_start到client_start+client_size之间的设置为Client,其它的设置为Device
MarkValidated(layers, client_start, client_size);
bool testing_needed = !(client_start == 0 && client_size == layers.size());
AtomicCommitArgs a_args = {.test_only = true};
if (testing_needed &&
display->CreateComposition(a_args) != HWC2::Error::None) {
++display->total_stats().failed_kms_validate_;
client_start = 0;
client_size = layers.size();
//设置合成类型,client_start到client_start+client_size之间的设置为Client,其它的设置为Device
MarkValidated(layers, 0, client_size);
}
}
*num_types = client_size;
display->total_stats().gpu_pixops_ += CalcPixOps(layers, client_start,
client_size);
display->total_stats().total_pixops_ += CalcPixOps(layers, 0, layers.size());
return *num_types != 0 ? HWC2::Error::HasChanges : HWC2::Error::None;
}
Backend中还有几个辅助方法,简单介绍下
GetClientLayers
:刷选出哪些layer需要Client合成,筛选是会经过两层考核 IsClientLayer & GetExtraClientRange
IsClientLayer
:判断指定的Layer是否要Client合成,有几个条件:1. HardwareSupportsLayerType硬件不支持的合成方式
2. IsHandleUsable buffer handle无法转为DRM要求的buffer object
3. color_transform_hint !=HAL_COLOR_TRANSFORM_IDENTITY
4. 需要scale or phase,但hwc强制GPU来处理
GetExtraClientRange
: 进一步筛选client layer, 当layer的数量多于hwc支持的planes时,需要留出一个给 client target
合成显示
PresentDisplay方法的作用就是把内容呈现到屏幕上去
[drm-hwcomposer/hwc2_device/HwcDisplay.cpp]
HWC2::Error HwcDisplay::PresentDisplay(int32_t *present_fence) {
...
AtomicCommitArgs a_args{};
ret = CreateComposition(a_args);// 调用
...
}
主要是去调用了CreateComposition这个方法
[drm-hwcomposer/hwc2_device/HwcDisplay.cpp]
HWC2::Error HwcDisplay::CreateComposition(AtomicCommitArgs &a_args) {
if (IsInHeadlessMode()) { // 无头模式,不做处理,返回
ALOGE("%s: Display is in headless mode, should never reach here", __func__);
return HWC2::Error::None;
}
int PrevModeVsyncPeriodNs = static_cast<int>(
1E9 / GetPipe().connector->Get()->GetActiveMode().v_refresh());
auto mode_update_commited_ = false; // 是否需要更新/提交
if (staged_mode_ && // staged_mode_ 当前所处的显示模式
staged_mode_change_time_ <= ResourceManager::GetTimeMonotonicNs()) {
client_layer_.SetLayerDisplayFrame( // 设置显示的位置大小
(hwc_rect_t){.left = 0,
.top = 0,
.right = static_cast<int>(staged_mode_->h_display()),
.bottom = static_cast<int>(staged_mode_->v_display())});
configs_.active_config_id = staged_mode_config_id_;
a_args.display_mode = *staged_mode_;
if (!a_args.test_only) {
mode_update_commited_ = true;
}
}
// order the layers by z-order
bool use_client_layer = false; // 是否有GPU合成的图层
uint32_t client_z_order = UINT32_MAX;
std::map<uint32_t, HwcLayer *> z_map;
for (std::pair<const hwc2_layer_t, HwcLayer> &l : layers_) {
switch (l.second.GetValidatedType()) {
case HWC2::Composition::Device:
z_map.emplace(std::make_pair(l.second.GetZOrder(), &l.second)); // z_map中是按照z-order排序的,Device合成的图层
break;
case HWC2::Composition::Client:
// Place it at the z_order of the lowest client layer
use_client_layer = true;
client_z_order = std::min(client_z_order, l.second.GetZOrder()); // 找到GPU合成图层中最小的z-order
break;
default:
continue;
}
}
if (use_client_layer)
z_map.emplace(std::make_pair(client_z_order, &client_layer_)); // GPU合成的Client图层加入z_map集合
if (z_map.empty()) // 空集合,没有要合成的图层
return HWC2::Error::BadLayer;
std::vector<DrmHwcLayer> composition_layers;
// now that they're ordered by z, add them to the composition
for (std::pair<const uint32_t, HwcLayer *> &l : z_map) {
DrmHwcLayer layer;
l.second->PopulateDrmLayer(&layer); // 把HwcLayer转为DrmHwcLayer,主要是一些信息
int ret = layer.ImportBuffer(GetPipe().device); // 1. 把buffer_handle_t转为drm buffer object
// 2. 做drmPrimeFDToHandle处理
if (ret) {
ALOGE("Failed to import layer, ret=%d", ret);
return HWC2::Error::NoResources;
}
composition_layers.emplace_back(std::move(layer));
}
/* Store plan to ensure shared planes won't be stolen by other display
* in between of ValidateDisplay() and PresentDisplay() calls
*/
current_plan_ = DrmKmsPlan::CreateDrmKmsPlan(GetPipe(), // 创建一个计划:合成显示
std::move(composition_layers));
if (!current_plan_) {
if (!a_args.test_only) {
ALOGE("Failed to create DrmKmsPlan");
}
return HWC2::Error::BadConfig;
}
a_args.composition = current_plan_;
// 提交/合成/显示到屏幕 == >DrmAtomicStateManager::ExecuteAtomicCommit
int ret = GetPipe().atomic_state_manager->ExecuteAtomicCommit(a_args);
if (ret) {
if (!a_args.test_only)
ALOGE("Failed to apply the frame composition ret=%d", ret);
return HWC2::Error::BadParameter;
}
if (mode_update_commited_) {
staged_mode_.reset();
vsync_tracking_en_ = false;
if (last_vsync_ts_ != 0) {
hwc2_->SendVsyncPeriodTimingChangedEventToClient(
handle_, last_vsync_ts_ + PrevModeVsyncPeriodNs);
}
}
return HWC2::Error::None;
}
上面出现了一个新的类型
struct DrmHwcLayer {
buffer_handle_t sf_handle = nullptr;
hwc_drm_bo_t buffer_info{};
std::shared_ptr<DrmFbIdHandle> fb_id_handle;
int gralloc_buffer_usage = 0;
DrmHwcTransform transform{};
DrmHwcBlending blending = DrmHwcBlending::kNone;
uint16_t alpha = UINT16_MAX;
hwc_frect_t source_crop;
hwc_rect_t display_frame;
DrmHwcColorSpace color_space;
DrmHwcSampleRange sample_range;
UniqueFd acquire_fence;
int ImportBuffer(DrmDevice *drm_device);
bool IsProtected() const {
return (gralloc_buffer_usage & GRALLOC_USAGE_PROTECTED) ==
GRALLOC_USAGE_PROTECTED;
}
};
ImportBuffer调用的流程:
int DrmHwcLayer::ImportBuffer(DrmDevice *drm_device) {
buffer_info = hwc_drm_bo_t{};
int ret = BufferInfoGetter::GetInstance()->ConvertBoInfo(sf_handle,
&buffer_info);
if (ret != 0) {
ALOGE("Failed to convert buffer info %d", ret);
return ret;
}
fb_id_handle = drm_device->GetDrmFbImporter().GetOrCreateFbId(&buffer_info);
if (!fb_id_handle) {
ALOGE("Failed to import buffer");
return -EINVAL;
}
return 0;
}
进而调用到相关方法
BufferInfoMapperMetadata::ConvertBoInfo
DrmFbImporter::GetOrCreateFbId
DrmAtomicStateManager::CommitFrame方法中应该是最终去显示内容的逻辑。
看一下CommitFrame调用栈信息:
PresentDisplay调用栈信息
ValidateDisplay调用栈信息