[librsvg/rustification] gradient.rs: Export functions to create Gradient objects and set their color stops

[Federico Mena Quintero <federico src gnome org>]

commit 370634f1491df627009128191ba2625fc9bbd473
Author: Federico Mena Quintero <federico gnome org>
Date:   Fri Nov 25 15:09:42 2016 -0600

    gradient.rs: Export functions to create Gradient objects and set their color stops
    
    We will use these from the *_fix_fallback() functions to do fallback
    resolution for gradients in the Rust code.

 rsvg-paint-server.h  |   22 +++++++++++++
 rust/src/gradient.rs |   84 ++++++++++++++++++++++++++++++++++++++++++++++++++
 rust/src/lib.rs      |    6 +++
 3 files changed, 112 insertions(+), 0 deletions(-)
---
diff --git a/rsvg-paint-server.h b/rsvg-paint-server.h
index bfc31ae..c1dcc64 100644
--- a/rsvg-paint-server.h
+++ b/rsvg-paint-server.h
@@ -84,6 +84,28 @@ struct _RsvgRadialGradient {
     char *fallback;
 };
 
+typedef struct _Gradient Gradient;
+
+/* Implemented in rust/src/gradient.rs */
+G_GNUC_INTERNAL
+Gradient *gradient_linear_new (RsvgLength     *x1,
+                               RsvgLength     *y1,
+                               RsvgLength     *x2,
+                               RsvgLength     *y2,
+                               gboolean       *obj_bbox,
+                               cairo_matrix_t *affine,
+                               cairo_extend_t *extend,
+                               const char     *fallback_name);
+
+/* Implemented in rust/src/gradient.rs */
+G_GNUC_INTERNAL
+void gradient_destroy (Gradient *gradient);
+
+G_GNUC_INTERNAL
+void gradient_add_color_stop (Gradient *gradient,
+                              double    offset,
+                              guint32   rgba);
+
 struct _RsvgPattern {
     RsvgNode super;
     gboolean obj_cbbox;
diff --git a/rust/src/gradient.rs b/rust/src/gradient.rs
index a68f21d..cab051a 100644
--- a/rust/src/gradient.rs
+++ b/rust/src/gradient.rs
@@ -1,5 +1,9 @@
+extern crate libc;
 extern crate cairo;
 extern crate cairo_sys;
+extern crate glib;
+
+use self::glib::translate::*;
 
 use length::*;
 
@@ -98,6 +102,29 @@ impl GradientCommon {
             self.fallback = clone_fallback_name (&fallback.fallback);
         }
     }
+
+    fn add_color_stop (&mut self, mut offset: f64, rgba: u32) {
+        if self.stops.is_none () {
+            self.stops = Some (Vec::<ColorStop>::new ());
+        }
+
+        if let Some (ref mut stops) = self.stops {
+            let mut last_offset: f64 = 0.0;
+
+            if stops.len () > 0 {
+                last_offset = stops[stops.len () - 1].offset;
+            }
+
+            if last_offset > offset {
+                offset = last_offset;
+            }
+
+            stops.push (ColorStop { offset: offset,
+                                    rgba:   rgba });
+        } else {
+            unreachable! ();
+        }
+    }
 }
 
 fn clone_fallback_name (fallback: &Option<String>) -> Option<String> {
@@ -196,6 +223,11 @@ impl Gradient {
         self.common.resolve_from_fallback (&fallback.common);
         self.variant.resolve_from_fallback (&fallback.variant);
     }
+
+    fn add_color_stop (&mut self, offset: f64, rgba: u32) {
+        self.common.add_color_stop (offset, rgba);
+    }
+
 }
 
 trait FallbackSource {
@@ -227,3 +259,55 @@ fn resolve_gradient (gradient: &Gradient, fallback_source: &FallbackSource) -> G
 
     result
 }
+
+/* All the arguments are pointers because they are in fact optional in
+ * SVG.  We turn the arguments into Option<foo>: NULL into None, and
+ * anything else into a Some().
+ */
+#[no_mangle]
+pub unsafe extern fn gradient_linear_new (x1: *const RsvgLength,
+                                          y1: *const RsvgLength,
+                                          x2: *const RsvgLength,
+                                          y2: *const RsvgLength,
+                                          obj_bbox: *const bool,
+                                          affine: *const cairo::Matrix,
+                                          spread: *const cairo::enums::Extend,
+                                          fallback_name: *const libc::c_char) -> *mut Gradient {
+    let my_obj_bbox      = { if obj_bbox.is_null ()      { None } else { Some (*obj_bbox) } };
+    let my_affine        = { if affine.is_null ()        { None } else { Some (*affine) } };
+    let my_spread        = { if spread.is_null ()        { None } else { Some (*spread) } };
+    let my_fallback_name = from_glib_none (fallback_name);
+
+    let my_x1 = { if x1.is_null () { None } else { Some (*x1) } };
+    let my_y1 = { if y1.is_null () { None } else { Some (*y1) } };
+    let my_x2 = { if x2.is_null () { None } else { Some (*x2) } };
+    let my_y2 = { if y2.is_null () { None } else { Some (*y2) } };
+
+    let gradient = Gradient::new (GradientCommon::new (my_obj_bbox, my_affine, my_spread, my_fallback_name, 
None),
+                                  GradientVariant::Linear { x1: my_x1,
+                                                            y1: my_y1,
+                                                            x2: my_x2,
+                                                            y2: my_y2 });
+
+    let boxed_gradient = Box::new (gradient);
+
+    Box::into_raw (boxed_gradient)
+}
+
+#[no_mangle]
+pub unsafe extern fn gradient_destroy (raw_gradient: *mut Gradient) {
+    assert! (!raw_gradient.is_null ());
+
+    let _ = Box::from_raw (raw_gradient);
+}
+
+#[no_mangle]
+pub extern fn gradient_add_color_stop (raw_gradient: *mut Gradient,
+                                       offset:       f64,
+                                       rgba:         u32) {
+    assert! (!raw_gradient.is_null ());
+
+    let gradient: &mut Gradient = unsafe { &mut (*raw_gradient) };
+
+    gradient.add_color_stop (offset, rgba);
+}
diff --git a/rust/src/lib.rs b/rust/src/lib.rs
index 2068691..f6ccfa7 100644
--- a/rust/src/lib.rs
+++ b/rust/src/lib.rs
@@ -1,3 +1,9 @@
+pub use gradient::{
+    gradient_linear_new,
+    gradient_destroy,
+    gradient_add_color_stop
+};
+
 pub use path_builder::{
     rsvg_path_builder_new,
     rsvg_path_builder_destroy,