Add a basic lines-based debug-renderer

src/pipeline/debug_render_pipeline/debug_render_backend.rs

@@ -0,0 +1,66 @@
+use crate::dynamics::{
+    ImpulseJoint, ImpulseJointHandle, Multibody, MultibodyLink, RigidBody, RigidBodyHandle,
+};
+use crate::geometry::Collider;
+use crate::math::{Isometry, Point, Real, Vector};
+use crate::prelude::{ColliderHandle, MultibodyJointHandle};
+use na::Scale;
+
+#[derive(Copy, Clone)]
+pub enum DebugRenderObject<'a> {
+    RigidBody(RigidBodyHandle, &'a RigidBody),
+    Collider(ColliderHandle, &'a Collider),
+    ImpulseJoint(ImpulseJointHandle, &'a ImpulseJoint),
+    MultibodyJoint(MultibodyJointHandle, &'a Multibody, &'a MultibodyLink),
+    Other,
+}
+
+pub trait DebugRenderBackend {
+    fn draw_line(
+        &mut self,
+        object: DebugRenderObject,
+        a: Point<Real>,
+        b: Point<Real>,
+        color: [f32; 4],
+    );
+
+    fn draw_polyline(
+        &mut self,
+        object: DebugRenderObject,
+        vertices: &[Point<Real>],
+        indices: &[[u32; 2]],
+        transform: &Isometry<Real>,
+        scale: &Vector<Real>,
+        color: [f32; 4],
+    ) {
+        for idx in indices {
+            let a = transform * (Scale::from(*scale) * vertices[idx[0] as usize]);
+            let b = transform * (Scale::from(*scale) * vertices[idx[1] as usize]);
+            self.draw_line(object, a, b, color);
+        }
+    }
+
+    fn draw_line_strip(
+        &mut self,
+        object: DebugRenderObject,
+        vertices: &[Point<Real>],
+        transform: &Isometry<Real>,
+        scale: &Vector<Real>,
+        color: [f32; 4],
+        closed: bool,
+    ) {
+        for vtx in vertices.windows(2) {
+            let a = transform * (Scale::from(*scale) * vtx[0]);
+            let b = transform * (Scale::from(*scale) * vtx[1]);
+            self.draw_line(object, a, b, color);
+        }
+
+        if closed {
+            if vertices.len() > 2 {
+                let a = transform * (Scale::from(*scale) * vertices[0]);
+                let b = transform * (Scale::from(*scale) * vertices.last().unwrap());
+                self.draw_line(object, a, b, color);
+            }
+        }
+    }
+}