scene: Decouple draw method from scene graph.

* sly/render/renderer.scm (transform-render-op): New procedure.
* sly/scene.scm (scene->renderer): Don't pass transform to draw method.
  Instead, transform the resulting render op afterwards.
* sly/mesh.scm (draw): Remove 'transform' parameter.

3 files changed, 14 insertions, 4 deletions

diff --git a/sly/mesh.scm b/sly/mesh.scm
index e662547..2a0c8ec 100644
--- a/sly/mesh.scm
+++ b/sly/mesh.scm
@@ -58,9 +58,8 @@
   (%make-mesh (make-vertex-array indices positions textures)
               shader texture))
 
-(define-method (draw (mesh <<mesh>>) transform)
+(define-method (draw (mesh <<mesh>>))
   (make-render-op #:vertex-array (mesh-vao mesh)
                   #:texture (mesh-texture mesh)
                   #:shader (mesh-shader mesh)
-                  #:uniforms `(("color" ,white))
-                  #:transform transform))
+                  #:uniforms `(("color" ,white))))
diff --git a/sly/render/renderer.scm b/sly/render/renderer.scm
index d71b89a..3584023 100644
--- a/sly/render/renderer.scm
+++ b/sly/render/renderer.scm
@@ -38,6 +38,7 @@
             render-op-transform render-op-vertex-array
             render-op-texture render-op-shader
             render-op-blend-mode render-op-uniforms
+            transform-render-op
             make-renderer renderer?
             renderer-ops
             render))
@@ -68,6 +69,15 @@ activated or not."
   (%make-render-op transform vertex-array texture shader uniforms
                    blend-mode depth-test?))
 
+(define* (transform-render-op op transform)
+  "Return a new render operation object that is the same as OP, but
+with its transformation matrix multiplied by TRANSFORM."
+  (match op
+    (($ <render-op> local-transform vertex-array texture shader uniforms
+                    blend-mode depth-test?)
+     (%make-render-op (transform* transform local-transform) vertex-array
+                      texture shader uniforms blend-mode depth-test?))))
+
 (define-syntax-rule (with-texture-maybe texture body ...)
   (if texture
       (with-texture texture body ...)
diff --git a/sly/scene.scm b/sly/scene.scm
index e068e60..6cd3a5d 100644
--- a/sly/scene.scm
+++ b/sly/scene.scm
@@ -78,7 +78,8 @@ display the scene."
                                        (scene-node-transform node)))
                 (object (scene-node-object node)))
             (cons (if object
-                      (draw (scene-node-object node) transform)
+                      (transform-render-op (draw (scene-node-object node))
+                                           transform)
                       '())
                   (map (cut iter <> transform)
                        (scene-node-children node))))