[librsvg/rustification] path_builder.rs: Start porting RsvgPathBuilder

[Federico Mena Quintero <federico src gnome org>]

commit e354165200256446aef64c56e892c831806afe6b
Author: Federico Mena Quintero <federico gnome org>
Date:   Mon Oct 31 21:59:54 2016 -0600

    path_builder.rs: Start porting RsvgPathBuilder
    
    We'll keep the entire C API of that function for now, as it
    is used from rsvg-shapes.c.

 rust/src/lib.rs          |   10 +++++
 rust/src/path_builder.rs |  100 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 110 insertions(+), 0 deletions(-)
---
diff --git a/rust/src/lib.rs b/rust/src/lib.rs
index 963ad74..5dc77a9 100644
--- a/rust/src/lib.rs
+++ b/rust/src/lib.rs
@@ -1,5 +1,15 @@
+pub use path_builder::{
+    rsvg_path_builder_new,
+    rsvg_path_builder_destroy,
+    rsvg_path_builder_move_to,
+    rsvg_path_builder_line_to,
+    rsvg_path_builder_curve_to,
+    rsvg_path_builder_close_path
+};
+
 pub use marker::{
     rsvg_rust_render_markers,
 };
 
+mod path_builder;
 mod marker;
diff --git a/rust/src/path_builder.rs b/rust/src/path_builder.rs
new file mode 100644
index 0000000..7cebce5
--- /dev/null
+++ b/rust/src/path_builder.rs
@@ -0,0 +1,100 @@
+extern crate cairo;
+
+#[repr(C)]
+pub struct RsvgPathBuilder {
+    path_data: Vec<cairo::PathSegment>,
+    last_move_to_index: Option<usize>
+}
+
+impl RsvgPathBuilder {
+    fn move_to (&mut self, x: f64, y: f64) {
+        self.path_data.push (cairo::PathSegment::MoveTo ((x, y)));
+        self.last_move_to_index = Some (self.path_data.len () - 1);
+    }
+
+    fn line_to (&mut self, x: f64, y: f64) {
+        self.path_data.push (cairo::PathSegment::LineTo ((x, y)));
+    }
+
+    fn curve_to (&mut self, x2: f64, y2: f64, x3: f64, y3: f64, x4: f64, y4: f64) {
+        self.path_data.push (cairo::PathSegment::CurveTo ((x2, y2), (x3, y3), (x4, y4)));
+    }
+
+    fn close_path (&mut self) {
+        if let Some (idx) = self.last_move_to_index {
+            let segment = self.path_data[idx];
+
+            if let cairo::PathSegment::MoveTo ((x, y)) = segment {
+                self.move_to (x, y);
+            } else {
+                unreachable! ();
+            }
+        }
+    }
+}
+
+#[no_mangle]
+pub unsafe extern fn rsvg_path_builder_new () -> *mut RsvgPathBuilder {
+    let builder = RsvgPathBuilder {
+        path_data: Vec::new (),
+        last_move_to_index: None
+    };
+
+    let boxed_builder = Box::new (builder);
+
+    Box::into_raw (boxed_builder)
+}
+
+#[no_mangle]
+pub unsafe extern fn rsvg_path_builder_destroy (raw_builder: *mut RsvgPathBuilder) {
+    assert! (!raw_builder.is_null ());
+
+    let _ = Box::from_raw (raw_builder);
+}
+
+#[no_mangle]
+pub extern fn rsvg_path_builder_move_to (raw_builder: *mut RsvgPathBuilder,
+                                         x: f64,
+                                         y: f64) {
+    assert! (!raw_builder.is_null ());
+
+    let builder: &mut RsvgPathBuilder;
+    unsafe { builder = &mut (*raw_builder); }
+
+    builder.move_to (x, y);
+}
+
+#[no_mangle]
+pub extern fn rsvg_path_builder_line_to (raw_builder: *mut RsvgPathBuilder,
+                                         x: f64,
+                                         y: f64) {
+    assert! (!raw_builder.is_null ());
+
+    let builder: &mut RsvgPathBuilder;
+    unsafe { builder = &mut (*raw_builder); }
+
+    builder.line_to (x, y);
+}
+
+#[no_mangle]
+pub extern fn rsvg_path_builder_curve_to (raw_builder: *mut RsvgPathBuilder,
+                                          x2: f64, y2: f64,
+                                          x3: f64, y3: f64,
+                                          x4: f64, y4: f64) {
+    assert! (!raw_builder.is_null ());
+
+    let builder: &mut RsvgPathBuilder;
+    unsafe { builder = &mut (*raw_builder); }
+
+    builder.curve_to (x2, y2, x3, y3, x4, y4);
+}
+
+#[no_mangle]
+pub extern fn rsvg_path_builder_close_path (raw_builder: *mut RsvgPathBuilder) {
+    assert! (!raw_builder.is_null ());
+
+    let builder: &mut RsvgPathBuilder;
+    unsafe { builder = &mut (*raw_builder); }
+
+    builder.close_path ();
+}