[librsvg] DrawingCtx::new() - set up the initial coordinate system per the spec

[Federico Mena Quintero <federico src gnome org>]

commit ee56c82a90dc2c0c607dfbe5afb9ab9325221c7f
Author: Federico Mena Quintero <federico gnome org>
Date:   Wed Feb 20 09:26:46 2019 -0600

    DrawingCtx::new() - set up the initial coordinate system per the spec
    
    This has (0, 0) at the upper-left corner of the viewport, and matches
    the viewport's size.  That is, the initial coordinate system is not
    concerned with the viewBox of the toplevel <svg> element.
    
    NodeSvg will handle its viewBox through its call to draw_in_viewport().

 rsvg_internals/src/drawing_ctx.rs | 26 +++++++++++++++++++-------
 rsvg_internals/src/handle.rs      | 19 +------------------
 2 files changed, 20 insertions(+), 25 deletions(-)
---
diff --git a/rsvg_internals/src/drawing_ctx.rs b/rsvg_internals/src/drawing_ctx.rs
index 8f966b70..630e7207 100644
--- a/rsvg_internals/src/drawing_ctx.rs
+++ b/rsvg_internals/src/drawing_ctx.rs
@@ -115,18 +115,12 @@ impl DrawingCtx {
         svg: Rc<Svg>,
         cr: &cairo::Context,
         viewport: &cairo::Rectangle,
-        vbox: &ViewBox,
         dpi: Dpi,
         testing: bool,
     ) -> DrawingCtx {
         let mut affine = cr.get_matrix();
         let rect = viewport.transform(&affine).outer();
 
-        // scale according to size set by size_func callback
-        let mut scale = cairo::Matrix::identity();
-        scale.scale(viewport.width / vbox.width, viewport.height / vbox.height);
-        affine = cairo::Matrix::multiply(&affine, &scale);
-
         // adjust transform so that the corner of the
         // bounding box above is at (0,0)
         affine.x0 -= rect.x;
@@ -134,7 +128,25 @@ impl DrawingCtx {
         cr.set_matrix(affine);
 
         let mut view_box_stack = Vec::new();
-        view_box_stack.push(*vbox);
+
+        // https://www.w3.org/TR/SVG2/coords.html#InitialCoordinateSystem
+        //
+        // "For the outermost svg element, the SVG user agent must
+        // determine an initial viewport coordinate system and an
+        // initial user coordinate system such that the two
+        // coordinates systems are identical. The origin of both
+        // coordinate systems must be at the origin of the SVG
+        // viewport."
+        //
+        // "... the initial viewport coordinate system (and therefore
+        // the initial user coordinate system) must have its origin at
+        // the top/left of the viewport"
+        view_box_stack.push(ViewBox {
+            x: 0.0,
+            y: 0.0,
+            width: viewport.width,
+            height: viewport.height,
+        });
 
         DrawingCtx {
             svg: svg.clone(),
diff --git a/rsvg_internals/src/handle.rs b/rsvg_internals/src/handle.rs
index 11d0b483..f79feb32 100644
--- a/rsvg_internals/src/handle.rs
+++ b/rsvg_internals/src/handle.rs
@@ -31,7 +31,6 @@ use structure::{IntrinsicDimensions, NodeSvg};
 use surface_utils::{shared_surface::SharedImageSurface, shared_surface::SurfaceType};
 use svg::Svg;
 use util::rsvg_g_warning;
-use viewbox::ViewBox;
 use xml::XmlState;
 use xml2_load::xml_state_load_from_possibly_compressed_stream;
 
@@ -295,14 +294,12 @@ impl Handle {
         &self,
         cr: &cairo::Context,
         viewport: &cairo::Rectangle,
-        vbox: &ViewBox,
         node: Option<&RsvgNode>,
     ) -> DrawingCtx {
         let mut draw_ctx = DrawingCtx::new(
             self.svg.borrow().as_ref().unwrap().clone(),
             cr,
             viewport,
-            vbox,
             self.dpi.get(),
             self.is_testing.get(),
         );
@@ -400,7 +397,6 @@ impl Handle {
                 width: f64::from(dimensions.width),
                 height: f64::from(dimensions.height),
             },
-            &ViewBox::new(0.0, 0.0, dimensions.em, dimensions.ex),
             Some(node),
         );
         let root = self.get_root();
@@ -536,7 +532,6 @@ impl Handle {
                 width: f64::from(dimensions.width),
                 height: f64::from(dimensions.height),
             },
-            &ViewBox::new(0.0, 0.0, dimensions.em, dimensions.ex),
             node.as_ref(),
         );
         let res = draw_ctx.draw_node_from_stack(&root.get_cascaded_values(), &root, false);
@@ -561,20 +556,8 @@ impl Handle {
 
         let root = self.get_root();
 
-        let svg_ref = self.svg.borrow();
-        let svg = svg_ref.as_ref().unwrap();
-
-        let dimensions = svg.get_intrinsic_dimensions();
-
-        let vbox = dimensions.vbox.unwrap_or_else(|| ViewBox {
-            x: 0.0,
-            y: 0.0,
-            width: viewport.width,
-            height: viewport.height,
-        });
-
         cr.save();
-        let mut draw_ctx = self.create_drawing_ctx_for_node(cr, viewport, &vbox, node.as_ref());
+        let mut draw_ctx = self.create_drawing_ctx_for_node(cr, viewport, node.as_ref());
         let res = draw_ctx.draw_node_from_stack(&root.get_cascaded_values(), &root, false);
         cr.restore();