Fix gtk3_native with nonzero origin.

Author: anntzer

lib/mplcairo/base.py

@@ -77,11 +77,11 @@ def __init__(self, width, height, dpi):
         RendererBase.__init__(self)
 
     @classmethod
-    def from_pycairo_ctx(cls, ctx, width, height, dpi):
+    def from_pycairo_ctx(cls, ctx, width, height, dpi, orig_scale):
         obj = _mplcairo.GraphicsContextRendererCairo.__new__(
-            cls, ctx, width, height, dpi)
+            cls, ctx, width, height, dpi, orig_scale)
         _mplcairo.GraphicsContextRendererCairo.__init__(
-            obj, ctx, width, height, dpi)
+            obj, ctx, width, height, dpi, orig_scale)
         RendererBase.__init__(obj)
         return obj
 

lib/mplcairo/gtk_native.py

@@ -29,7 +29,7 @@ def on_draw_event(self, widget, ctx):
         # a RecordingSurface).
         renderer = self._get_cached_or_new_renderer(
             GraphicsContextRendererCairo.from_pycairo_ctx,
-            ctx, figure.bbox.width, figure.bbox.height, figure.dpi)
+            ctx, figure.bbox.width, figure.bbox.height, figure.dpi, prev_scale)
         figure.draw(renderer)
         surface.set_device_scale(*prev_scale)
 

src/_mplcairo.cpp

@@ -171,7 +171,7 @@ GraphicsContextRenderer::AdditionalContext::AdditionalContext(
   if (auto const& rectangle = state.clip_rectangle) {
     auto const& [x, y, w, h] = *rectangle;
     cairo_save(cr);
-    cairo_identity_matrix(cr);
+    restore_init_matrix(cr);
     cairo_new_path(cr);
     cairo_rectangle(cr, x, state.height - h - y, w, h);
     cairo_restore(cr);
@@ -192,6 +192,7 @@ GraphicsContextRenderer::AdditionalContext::AdditionalContext(
           "cairo_tag_begin requires cairo>=1.15.4");
     }
   }
+  restore_init_matrix(cr);
 }
 
 GraphicsContextRenderer::AdditionalContext::~AdditionalContext()
@@ -313,7 +314,8 @@ GraphicsContextRenderer::GraphicsContextRenderer(
     std::floor(width), std::floor(height), dpi}
 {}
 
-cairo_t* GraphicsContextRenderer::cr_from_pycairo_ctx(py::object ctx)
+cairo_t* GraphicsContextRenderer::cr_from_pycairo_ctx(
+  py::object ctx, std::tuple<double, double> device_scales)
 {
   if (!detail::has_pycairo) {
     throw std::runtime_error{"pycairo is not available"};
@@ -326,12 +328,24 @@ cairo_t* GraphicsContextRenderer::cr_from_pycairo_ctx(py::object ctx)
   auto const& cr = PycairoContext_GET(ctx.ptr());
   CAIRO_CHECK(cairo_status, cr);
   cairo_reference(cr);
+  // With native Gtk3, the context may have a nonzero initial translation (if
+  // the drawn area is not at the top left of the window); this needs to be
+  // taken into account by the path loader (which works in absolute coords).
+  auto mtx = new cairo_matrix_t{};
+  cairo_get_matrix(cr, mtx);
+  auto const& [sx, sy] = device_scales;
+  mtx->x0 *= sx; mtx->y0 *= sy;
+  CAIRO_CHECK_SET_USER_DATA(
+    cairo_set_user_data, cr, &detail::INIT_MATRIX_KEY, mtx,
+    [](void* data) -> void { delete static_cast<cairo_matrix_t*>(data); });
   return cr;
 }
 
 GraphicsContextRenderer::GraphicsContextRenderer(
-  py::object ctx, double width, double height, double dpi) :
-  GraphicsContextRenderer{cr_from_pycairo_ctx(ctx), width, height, dpi}
+  py::object ctx, double width, double height, double dpi,
+  std::tuple<double, double> device_scales) :
+  GraphicsContextRenderer{
+    cr_from_pycairo_ctx(ctx, device_scales), width, height, dpi}
 {}
 
 cairo_t* GraphicsContextRenderer::cr_from_fileformat_args(
@@ -2065,7 +2079,7 @@ Only intended for debugging purposes.
     // The RendererAgg signature, which is also expected by MixedModeRenderer
     // (with doubles!).
     .def(py::init<double, double, double>())
-    .def(py::init<py::object, double, double, double>())
+    .def(py::init<py::object, double, double, double, std::tuple<double, double>>())
     .def(py::init<StreamSurfaceType, py::object, double, double, double>())
     .def(
       py::pickle(

src/_mplcairo.h

@@ -51,10 +51,12 @@ class GraphicsContextRenderer {
 
   static cairo_t* cr_from_image_args(int width, int height);
   GraphicsContextRenderer(double width, double height, double dpi);
-  static cairo_t* cr_from_pycairo_ctx(py::object ctx);
+  static cairo_t* cr_from_pycairo_ctx(
+    py::object ctx, std::tuple<double, double> device_scales);
   GraphicsContextRenderer(
     py::object ctx,
-    double width, double height, double dpi);
+    double width, double height, double dpi,
+    std::tuple<double, double> device_scales);
   static cairo_t* cr_from_fileformat_args(
     StreamSurfaceType type, py::object file,
     double width, double height, double dpi);

src/_util.cpp

@@ -45,8 +45,12 @@ ITER_CAIRO_OPTIONAL_API(DEFINE_API)
 
 // Other useful values.
 std::unordered_map<std::string, cairo_font_face_t*> FONT_CACHE{};
-cairo_user_data_key_t const
-  REFS_KEY{}, STATE_KEY{}, FT_KEY{}, FEATURES_KEY{}, IS_COLOR_FONT_KEY{};
+cairo_user_data_key_t const REFS_KEY{},
+                            STATE_KEY{},
+                            INIT_MATRIX_KEY{},
+                            FT_KEY{},
+                            FEATURES_KEY{},
+                            IS_COLOR_FONT_KEY{};
 py::object RC_PARAMS{},
            PIXEL_MARKER{},
            UNIT_CIRCLE{};
@@ -191,6 +195,16 @@ AdditionalState& get_additional_state(cairo_t* cr)
   return stack.top();
 }
 
+void restore_init_matrix(cairo_t* cr)
+{
+  auto const& data = cairo_get_user_data(cr, &detail::INIT_MATRIX_KEY);
+  if (!data) {
+    cairo_identity_matrix(cr);
+  } else {
+    cairo_set_matrix(cr, static_cast<cairo_matrix_t*>(data));
+  }
+}
+
 // Set the current path of `cr` to `path`, after transformation by `matrix`,
 // ignoring the CTM ("exact").
 //
@@ -226,7 +240,7 @@ struct LoadPathContext {
     snap{!has_vector_surface(cr) && get_additional_state(cr).snap}
   {
     cairo_get_matrix(cr, &ctm);
-    cairo_identity_matrix(cr);
+    restore_init_matrix(cr);
     cairo_new_path(cr);
     auto const& lw = cairo_get_line_width(cr);
     snapper =
@@ -567,7 +581,7 @@ void fill_and_stroke_exact(
       load_path_exact(cr, path, matrix);
       path_loaded = true;
     }
-    cairo_identity_matrix(cr);  // Dashes are interpreted using the CTM.
+    restore_init_matrix(cr);  // Dashes are interpreted using the CTM.
     cairo_stroke_preserve(cr);
   }
   cairo_restore(cr);

src/_util.h

@@ -70,6 +70,7 @@ extern std::unordered_map<std::string, cairo_font_face_t*> FONT_CACHE;
 extern cairo_user_data_key_t const
   REFS_KEY,           // cairo_t -> kept alive Python objects.
   STATE_KEY,          // cairo_t -> additional state.
+  INIT_MATRIX_KEY,    // cairo_t -> cairo_matrix_t.
   FT_KEY,             // cairo_font_face_t -> FT_Face.
   FEATURES_KEY,       // cairo_font_face_t -> OpenType features.
   IS_COLOR_FONT_KEY;  // cairo_font_face_t -> non-null if a color font.
@@ -136,6 +137,7 @@ cairo_matrix_t matrix_from_transform(
   py::object transform, cairo_matrix_t const* master_matrix);
 bool has_vector_surface(cairo_t* cr);
 AdditionalState& get_additional_state(cairo_t* cr);
+void restore_init_matrix(cairo_t* cr);
 void load_path_exact(
   cairo_t* cr, py::object path, cairo_matrix_t const* matrix);
 void load_path_exact(