[librsvg: 72/90] Compute all of the affines in the same place

[Federico Mena Quintero <federico src gnome org>]

commit a44837e45f152c1953cf79f33740b0d93f63ed2b
Author: Federico Mena Quintero <federico gnome org>
Date:   Thu Mar 21 18:42:03 2019 -0600

    Compute all of the affines in the same place

 rsvg_internals/src/drawing_ctx.rs | 42 +++++++++++++++++++++++++++------------
 1 file changed, 29 insertions(+), 13 deletions(-)
---
diff --git a/rsvg_internals/src/drawing_ctx.rs b/rsvg_internals/src/drawing_ctx.rs
index 2031ef67..ab2b1227 100644
--- a/rsvg_internals/src/drawing_ctx.rs
+++ b/rsvg_internals/src/drawing_ctx.rs
@@ -463,6 +463,8 @@ impl DrawingCtx {
                     && enable_background == EnableBackground::Accumulate);
 
                 if needs_temporary_surface {
+                    // Compute our assortment of affines
+
                     let stack_was_empty = dc.cr_stack.len() == 0;
 
                     let affine = if stack_was_empty {
@@ -472,14 +474,6 @@ impl DrawingCtx {
                         cairo::Matrix::multiply(&affine_at_start, &initial_inverse)
                     };
 
-                    let cr = if filter.is_some() {
-                        cairo::Context::new(&dc.create_surface_for_toplevel_viewport()?)
-                    } else {
-                        cairo::Context::new(
-                            &dc.create_similar_surface_for_toplevel_viewport(&dc.cr.get_target())?,
-                        )
-                    };
-
                     let temporary_affine = if stack_was_empty {
                         let initial_inverse = dc.initial_affine_with_offset().try_invert().unwrap();
                         let untransformed = cairo::Matrix::multiply(&affine, &initial_inverse);
@@ -488,17 +482,37 @@ impl DrawingCtx {
                         affine_at_start
                     };
 
+                    let paint_affine = if stack_was_empty {
+                        dc.initial_affine_with_offset()
+                    } else {
+                        cairo::Matrix::identity()
+                    };
+
+                    // Create temporary surface and its cr
+
+                    let cr = if filter.is_some() {
+                        cairo::Context::new(&dc.create_surface_for_toplevel_viewport()?)
+                    } else {
+                        cairo::Context::new(
+                            &dc.create_similar_surface_for_toplevel_viewport(&dc.cr.get_target())?,
+                        )
+                    };
+
                     cr.set_matrix(temporary_affine);
 
                     dc.cr_stack.push(dc.cr.clone());
                     dc.cr = cr;
 
+                    // Create temporary bbox with the cr's affine
+
                     let prev_bbox = dc.bbox;
 
                     dc.bbox = BoundingBox::new(&temporary_affine);
 
                     let mut res = draw_fn(dc);
 
+                    // Filter
+
                     let source_surface = if let Some(filter_uri) = filter {
                         let child_surface =
                             cairo::ImageSurface::from(dc.cr.get_target()).unwrap();
@@ -512,18 +526,18 @@ impl DrawingCtx {
 
                     dc.cr = dc.cr_stack.pop().unwrap();
 
-                    let paint_affine = if stack_was_empty {
-                        dc.initial_affine_with_offset()
-                    } else {
-                        cairo::Matrix::identity()
-                    };
+                    // Set temporary surface as source
 
                     dc.cr.set_matrix(paint_affine);
                     dc.cr.set_source_surface(&source_surface, 0.0, 0.0);
 
+                    // Clip
+
                     dc.cr.set_matrix(affine);
                     dc.clip_to_node(&clip_in_object_space)?;
 
+                    // Mask
+
                     if let Some(mask) = mask {
                         if let Some(acquired) =
                             dc.get_acquired_node_of_type(Some(mask), NodeType::Mask)
@@ -544,6 +558,8 @@ impl DrawingCtx {
                             );
                         }
                     } else {
+                        // No mask, so composite the temporary surface
+
                         dc.cr.set_matrix(paint_affine);
 
                         if opacity < 1.0 {