dwrite: Re-add background geometry combine

If glyphrun unit is changed in a single line, there could be
overlapped background area which result in drawing background
twice. Adding geometry combine so that background geometry objects
with the same color can be merged and rendered at once

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5179>

subprojects/gst-plugins-bad/sys/dwrite/gstdwrite-renderer.cpp

@@ -43,9 +43,52 @@ struct RenderContext
   ID2D1Factory *factory;
   ID2D1RenderTarget *target;
   RECT client_rect;
+  std::vector<DWRITE_LINE_METRICS> line_metrics;
+  UINT line_index = 0;
+  UINT char_index = 0;
+  ComPtr<ID2D1Geometry> bg_rect;
+  D2D1_COLOR_F bg_color = D2D1::ColorF (D2D1::ColorF::Black, 0.0);
 };
 /* *INDENT-ON* */
 
+static HRESULT
+CombineTwoGeometries (ID2D1Factory * factory, ID2D1Geometry * a,
+    ID2D1Geometry * b, ID2D1Geometry ** result)
+{
+  HRESULT hr;
+  ComPtr < ID2D1GeometrySink > sink;
+  ComPtr < ID2D1PathGeometry > geometry;
+
+  hr = factory->CreatePathGeometry (&geometry);
+  if (FAILED (hr)) {
+    GST_WARNING ("Couldn't create path geometry, 0x%x", (guint) hr);
+    return hr;
+  }
+
+  hr = geometry->Open (&sink);
+  if (FAILED (hr)) {
+    GST_WARNING ("Couldn't open path geometry, 0x%x", (guint) hr);
+    return hr;
+  }
+
+  hr = a->CombineWithGeometry (b,
+      D2D1_COMBINE_MODE_UNION, nullptr, sink.Get ());
+  if (FAILED (hr)) {
+    GST_WARNING ("Couldn't combine geometry, 0x%x", (guint) hr);
+    return hr;
+  }
+
+  hr = sink->Close ();
+  if (FAILED (hr)) {
+    GST_WARNING ("Couldn't close sink, 0x%x", (guint) hr);
+    return hr;
+  }
+
+  *result = geometry.Detach ();
+
+  return S_OK;
+}
+
 STDMETHODIMP
     IGstDWriteTextRenderer::CreateInstance (IDWriteFactory * factory,
     IGstDWriteTextRenderer ** renderer)
@@ -179,13 +222,17 @@ STDMETHODIMP
     FLOAT adjust, ascent, descent;
     D2D1_RECT_F bg_rect;
     ComPtr < ID2D1SolidColorBrush > bg_brush;
+    DWRITE_LINE_METRICS line_metrics =
+        render_ctx->line_metrics.at (render_ctx->line_index);
 
-    if (!effect)
+    if (effect &&
-      return S_OK;
+        render_ctx->char_index + line_metrics.trailingWhitespaceLength <
-
+        line_metrics.length) {
       effect->GetBrushColor (GST_DWRITE_BRUSH_BACKGROUND, &color, &enabled);
-    if (!enabled)
+      if (enabled) {
-      return S_OK;
+        ComPtr < ID2D1RectangleGeometry > rect_geometry;
+        ComPtr < ID2D1PathGeometry > path_geometry;
+        ComPtr < ID2D1GeometrySink > path_sink;
 
         for (UINT32 i = 0; i < glyph_run->glyphCount; i++)
           run_width += glyph_run->glyphAdvances[i];
@@ -195,12 +242,59 @@ STDMETHODIMP
         ascent = adjust * font_metrics.ascent;
         descent = adjust * font_metrics.descent;
 
-    bg_rect = D2D1::RectF (origin_x, origin_y - ascent, origin_x + run_width,
+        bg_rect =
+            D2D1::RectF (origin_x, origin_y - ascent, origin_x + run_width,
             origin_y + descent);
 
-    target->CreateSolidColorBrush (color, &bg_brush);
+        hr = factory->CreateRectangleGeometry (bg_rect, &rect_geometry);
-    target->FillRectangle (bg_rect, bg_brush.Get ());
+        if (FAILED (hr))
-    target->DrawRectangle (bg_rect, bg_brush.Get ());
+          return hr;
+
+        hr = factory->CreatePathGeometry (&path_geometry);
+        if (FAILED (hr))
+          return hr;
+
+        hr = path_geometry->Open (&path_sink);
+        if (FAILED (hr))
+          return hr;
+
+        hr = rect_geometry->Outline (nullptr, path_sink.Get ());
+        if (FAILED (hr))
+          return hr;
+
+        path_sink->Close ();
+
+        if (render_ctx->bg_rect) {
+          if (render_ctx->bg_color.r == color.r &&
+              render_ctx->bg_color.g == color.g &&
+              render_ctx->bg_color.b == color.b &&
+              render_ctx->bg_color.a == color.a) {
+            ComPtr < ID2D1Geometry > combined;
+            hr = CombineTwoGeometries (factory,
+                render_ctx->bg_rect.Get (), path_geometry.Get (), &combined);
+            if (FAILED (hr))
+              return hr;
+
+            render_ctx->bg_rect = combined;
+          } else {
+            target->CreateSolidColorBrush (render_ctx->bg_color, &bg_brush);
+            target->FillGeometry (render_ctx->bg_rect.Get (), bg_brush.Get ());
+            render_ctx->bg_rect = nullptr;
+          }
+        }
+
+        if (!render_ctx->bg_rect) {
+          render_ctx->bg_rect = path_geometry;
+          render_ctx->bg_color = color;
+        }
+      }
+    }
+
+    render_ctx->char_index += glyph_run_desc->stringLength;
+    if (render_ctx->char_index >= line_metrics.length) {
+      render_ctx->line_index++;
+      render_ctx->char_index = 0;
+    }
 
     return S_OK;
   }
@@ -509,10 +603,21 @@ STDMETHODIMP
   HRESULT hr;
   RenderContext context;
   ComPtr < ID2D1Factory > d2d_factory;
+  UINT32 num_lines = 0;
 
   g_return_val_if_fail (layout != nullptr, E_INVALIDARG);
   g_return_val_if_fail (target != nullptr, E_INVALIDARG);
 
+  hr = layout->GetLineMetrics (nullptr, 0, &num_lines);
+  if (hr != E_NOT_SUFFICIENT_BUFFER)
+    return hr;
+
+  context.line_metrics.resize (num_lines);
+  hr = layout->GetLineMetrics (&context.line_metrics[0],
+      context.line_metrics.size (), &num_lines);
+  if (FAILED (hr))
+    return hr;
+
   target->GetFactory (&d2d_factory);
   context.render_path = RenderPath::BACKGROUND;
   context.client_rect = client_rect;
@@ -521,6 +626,18 @@ STDMETHODIMP
 
   hr = layout->Draw (&context, this, origin.x, origin.y);
 
+  if (FAILED (hr)) {
+    GST_WARNING ("Background Draw failed with 0x%x", (guint) hr);
+    return hr;
+  }
+
+  if (context.bg_rect) {
+    ComPtr < ID2D1SolidColorBrush > bg_brush;
+    target->CreateSolidColorBrush (context.bg_color, &bg_brush);
+    target->FillGeometry (context.bg_rect.Get (), bg_brush.Get ());
+    context.bg_rect = nullptr;
+  }
+
   context.render_path = RenderPath::TEXT;
   hr = layout->Draw (&context, this, origin.x, origin.y);