render: sprite-batch: Clean up sprite-batch-add!

* sly/render/sprite-batch.scm (sprite-batch-add!): Take better advantage
  of local variables to reduce lookups, add a comment, and reformat.

1 files changed, 63 insertions, 105 deletions

diff --git a/sly/render/sprite-batch.scm b/sly/render/sprite-batch.scm
index 1f591c2..8b59cb3 100644
--- a/sly/render/sprite-batch.scm
+++ b/sly/render/sprite-batch.scm
@@ -91,114 +91,72 @@
     (sprite-batch-flush! batch context)
     (sprite-batch-begin! batch))
 
+  ;; Establish the texture to use if this is the first sprite in the
+  ;; current batch.
   (when (texture-null? (sprite-batch-texture batch))
     (set-sprite-batch-texture! batch texture))
 
-  (let* ((size          (sprite-batch-size batch))
-         (index-offset  (* size 6))
-         (index-vertex-offset (* size 4))
-         (vertex-offset (* size 12)) ; 4 vertices, 3 floats per vertex
-         (texture-offset (* size 8))
-         (index-buffer (vertex-buffer-data
-                        (sprite-batch-index-buffer batch)))
-         (pos-buffer (vertex-buffer-data
-                      (sprite-batch-position-buffer batch)))
-         (tex-buffer (vertex-buffer-data
-                      (sprite-batch-texture-buffer batch))))
-
-    ;; Add indices.
-    (u32vector-set! index-buffer
-                    index-offset
-                    index-vertex-offset)
-    (u32vector-set! index-buffer
-                    (+ index-offset 1)
-                    (+ index-vertex-offset 3))
-    (u32vector-set! index-buffer
-                    (+ index-offset 2)
-                    (+ index-vertex-offset 2))
-    (u32vector-set! index-buffer
-                    (+ index-offset 3)
-                    index-vertex-offset)
-    (u32vector-set! index-buffer
-                    (+ index-offset 4)
-                    (+ index-vertex-offset 2))
-    (u32vector-set! index-buffer
-                    (+ index-offset 5)
-                    (+ index-vertex-offset 1))
-
-    ;; Add vertices.
-    ;; Bottom-left
-    (f32vector-set! pos-buffer
-                    vertex-offset
-                    (rect-left rect))
-    (f32vector-set! pos-buffer
-                    (+ vertex-offset 1)
-                    (rect-bottom rect))
-    (f32vector-set! pos-buffer
-                    (+ vertex-offset 2)
-                    0)
-    ;; Bottom-right
-    (f32vector-set! pos-buffer
-                    (+ vertex-offset 3)
-                    (rect-right rect))
-    (f32vector-set! pos-buffer
-                    (+ vertex-offset 4)
-                    (rect-bottom rect))
-    (f32vector-set! pos-buffer
-                    (+ vertex-offset 5)
-                    0)
-    ;; Top-right
-    (f32vector-set! pos-buffer
-                    (+ vertex-offset 6)
-                    (rect-right rect))
-    (f32vector-set! pos-buffer
-                    (+ vertex-offset 7)
-                    (rect-top rect))
-    (f32vector-set! pos-buffer
-                    (+ vertex-offset 8)
-                    0)
-    ;; Top-left
-    (f32vector-set! pos-buffer
-                    (+ vertex-offset 9)
-                    (rect-left rect))
-    (f32vector-set! pos-buffer
-                    (+ vertex-offset 10)
-                    (rect-top rect))
-    (f32vector-set! pos-buffer
-                    (+ vertex-offset 11)
-                    0)
-
-    ;; Add texture coordinates.
-    ;; Bottom-left
-    (f32vector-set! tex-buffer
-                    texture-offset
-                    (texture-s1 texture))
-    (f32vector-set! tex-buffer
-                    (+ texture-offset 1)
-                    (texture-t1 texture))
-    ;; Bottom-right
-    (f32vector-set! tex-buffer
-                    (+ texture-offset 2)
-                    (texture-s2 texture))
-    (f32vector-set! tex-buffer
-                    (+ texture-offset 3)
-                    (texture-t1 texture))
-    ;; Top-right
-    (f32vector-set! tex-buffer
-                    (+ texture-offset 4)
-                    (texture-s2 texture))
-    (f32vector-set! tex-buffer
-                    (+ texture-offset 5)
-                    (texture-t2 texture))
-    ;; Top-left
-    (f32vector-set! tex-buffer
-                    (+ texture-offset 6)
-                    (texture-s1 texture))
-    (f32vector-set! tex-buffer
-                    (+ texture-offset 7)
-                    (texture-t2 texture))
-
-    (set-sprite-batch-size! batch (1+ size))))
+  (let ((size (sprite-batch-size batch)))
+    (let ((index-offset  (* size 6))
+          (index-vertex-offset (* size 4))
+          (vertex-offset (* size 12)) ; 4 vertices, 3 floats per vertex
+          (texture-offset (* size 8))
+          (index-buffer (vertex-buffer-data
+                         (sprite-batch-index-buffer batch)))
+          (pos-buffer (vertex-buffer-data
+                       (sprite-batch-position-buffer batch)))
+          (tex-buffer (vertex-buffer-data
+                       (sprite-batch-texture-buffer batch)))
+          (s1 (texture-s1 texture))
+          (t1 (texture-t1 texture))
+          (s2 (texture-s2 texture))
+          (t2 (texture-t2 texture))
+          (top (rect-top rect))
+          (bottom (rect-bottom rect))
+          (left (rect-left rect))
+          (right (rect-right rect)))
+
+      ;; Add indices.
+      (u32vector-set! index-buffer index-offset index-vertex-offset)
+      (u32vector-set! index-buffer (+ index-offset 1) (+ index-vertex-offset 3))
+      (u32vector-set! index-buffer (+ index-offset 2) (+ index-vertex-offset 2))
+      (u32vector-set! index-buffer (+ index-offset 3) index-vertex-offset)
+      (u32vector-set! index-buffer (+ index-offset 4) (+ index-vertex-offset 2))
+      (u32vector-set! index-buffer (+ index-offset 5) (+ index-vertex-offset 1))
+
+      ;; Add vertices.
+      ;; Bottom-left
+      (f32vector-set! pos-buffer vertex-offset left)
+      (f32vector-set! pos-buffer (+ vertex-offset 1) bottom)
+      (f32vector-set! pos-buffer (+ vertex-offset 2) 0.0)
+      ;; Bottom-right
+      (f32vector-set! pos-buffer (+ vertex-offset 3) right)
+      (f32vector-set! pos-buffer (+ vertex-offset 4) bottom)
+      (f32vector-set! pos-buffer (+ vertex-offset 5) 0.0)
+      ;; Top-right
+      (f32vector-set! pos-buffer (+ vertex-offset 6) right)
+      (f32vector-set! pos-buffer (+ vertex-offset 7) top)
+      (f32vector-set! pos-buffer (+ vertex-offset 8) 0.0)
+      ;; Top-left
+      (f32vector-set! pos-buffer (+ vertex-offset 9) left)
+      (f32vector-set! pos-buffer (+ vertex-offset 10) top)
+      (f32vector-set! pos-buffer (+ vertex-offset 11) 0.0)
+
+      ;; Add texture coordinates.
+      ;; Bottom-left
+      (f32vector-set! tex-buffer texture-offset s1)
+      (f32vector-set! tex-buffer (+ texture-offset 1) t1)
+      ;; Bottom-right
+      (f32vector-set! tex-buffer (+ texture-offset 2) s2)
+      (f32vector-set! tex-buffer (+ texture-offset 3) t1)
+      ;; Top-right
+      (f32vector-set! tex-buffer (+ texture-offset 4) s2)
+      (f32vector-set! tex-buffer (+ texture-offset 5) t2)
+      ;; Top-left
+      (f32vector-set! tex-buffer (+ texture-offset 6) s1)
+      (f32vector-set! tex-buffer (+ texture-offset 7) t2)
+
+      (set-sprite-batch-size! batch (1+ size)))))
 
 (define (sprite-batch-reset! batch)
   "Reset BATCH to size 0."