commit 30808a20bb364267f7da95ee07a78e244049089d
author Lucas Berthou <berlu@google.com> Wed Feb 05 17:52:33 2025 +0000
committer Lucas Berthou <berlu@google.com> Tue Feb 18 17:19:38 2025 +0000
tree fee388667e50f74f13e2f56b56f470a1d0881da7
parent 75855a6ab877011a2e26ae95da7ddf06dd3a04b2

drm_hwcomposer: uses edid DTD to get better estimate of dpi

Edid are not the most reliable when it comes to panel size, however it
seems like preferred DTD are slightly more reliable. This change moves
from the drm parse edid display size to the first preferred DTD to try
improve dpi accuracy.
If no preferred DTD is available we still fallback to the display size.

Change-Id: Ibcc95da9f38ba74e9b95b9d68587b38efbed8de2
signed-off-by: Lucas Berthou <berlu@google.com>

hwc3/ComposerClient.cpp

diff --git a/hwc3/ComposerClient.cpp b/hwc3/ComposerClient.cpp
index 50d8ce6..7f3bc00 100644
--- a/hwc3/ComposerClient.cpp
+++ b/hwc3/ComposerClient.cpp
@@ -271,7 +271,7 @@
 #endif
 
 DisplayConfiguration HwcDisplayConfigToAidlConfiguration(
-    const HwcDisplayConfigs& configs, const HwcDisplayConfig& config) {
+    int32_t width, int32_t height, const HwcDisplayConfig& config) {
   DisplayConfiguration aidl_configuration =
       {.configId = static_cast<int32_t>(config.id),
        .width = config.mode.GetRawMode().hdisplay,
@@ -279,15 +279,14 @@
        .configGroup = static_cast<int32_t>(config.group_id),
        .vsyncPeriod = config.mode.GetVSyncPeriodNs()};
 
-  if (configs.mm_width != 0) {
-    // ideally this should be vdisplay/mm_heigth, however mm_height
-    // comes from edid parsing and is highly unreliable. Viewing the
-    // rarity of anisotropic displays, falling back to a single value
-    // for dpi yield more correct output.
+  if (width > 0) {
     static const float kMmPerInch = 25.4;
-    float dpi = float(config.mode.GetRawMode().hdisplay) * kMmPerInch /
-                float(configs.mm_width);
-    aidl_configuration.dpi = {.x = dpi, .y = dpi};
+    float dpi_x = float(config.mode.GetRawMode().hdisplay) * kMmPerInch /
+                float(width);
+    float dpi_y = height <= 0 ? dpi_x :
+                  float(config.mode.GetRawMode().vdisplay) * kMmPerInch /
+                    float(height);
+    aidl_configuration.dpi = {.x = dpi_x, .y = dpi_y};
   }
   // TODO: Populate vrrConfig.
   return aidl_configuration;
@@ -838,9 +837,11 @@
     return ToBinderStatus(hwc3::Error::kBadConfig);
   }
 
-  DisplayConfiguration
-      aidl_configuration = HwcDisplayConfigToAidlConfiguration(configs,
-                                                               config->second);
+  const auto bounds = display->GetDisplayBoundsMm();
+  DisplayConfiguration aidl_configuration =
+      HwcDisplayConfigToAidlConfiguration(/*width =*/ bounds.first,
+                                          /*height =*/bounds.second,
+                                          config->second);
   // Legacy API for querying DPI uses units of dots per 1000 inches.
   static const int kLegacyDpiUnit = 1000;
   switch (attribute) {
@@ -1419,9 +1420,12 @@
   }
 
   const HwcDisplayConfigs& configs = display->GetDisplayConfigs();
+  const auto bounds = display->GetDisplayBoundsMm();
   for (const auto& [id, config] : configs.hwc_configs) {
     configurations->push_back(
-        HwcDisplayConfigToAidlConfiguration(configs, config));
+        HwcDisplayConfigToAidlConfiguration(/*width =*/ bounds.first, 
+                                            /*height =*/ bounds.second,
+                                            config));
   }
   return ndk::ScopedAStatus::ok();
 }