From e68f6d4bf5e976a14918d1e7d902737be4a5e453 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Thu, 27 Jun 2013 22:36:50 -0400
Subject: Update particles example to use sprite batching.

---
 examples/particles.scm | 44 ++++++++++++++++++--------------------------
 1 file changed, 18 insertions(+), 26 deletions(-)

diff --git a/examples/particles.scm b/examples/particles.scm
index 39e2ae7..90bd010 100644
--- a/examples/particles.scm
+++ b/examples/particles.scm
@@ -26,29 +26,6 @@
   (position particle-position set-particle-position!)
   (velocity particle-velocity set-particle-velocity!))
 
-(define (draw-particle particle)
-  (let* ((texture (sprite-texture (particle-sprite particle)))
-         (p (particle-position particle))
-         (x (vx p))
-         (y (vy p))
-         (x2 (+ x (texture-width texture)))
-         (y2 (+ y (texture-height texture))))
-    (gl-texture-coordinates 0 0)
-    (gl-vertex x y)
-    (gl-texture-coordinates 1 0)
-    (gl-vertex x2 y)
-    (gl-texture-coordinates 1 1)
-    (gl-vertex x2 y2)
-    (gl-texture-coordinates 0 1)
-    (gl-vertex x y2)))
-
-(define (draw-particles particles)
-  (let ((texture (sprite-texture (particle-sprite (car particles)))))
-    (with-gl-bind-texture (texture-target texture-2d) (texture-id texture)
-      (gl-begin (begin-mode quads)
-        (gl-color 1 1 1)
-        (for-each (lambda (p) (draw-particle p)) particles)))))
-
 (define (update-particle! particle)
   (set-particle-position! particle
                           (v+ (particle-position particle)
@@ -65,15 +42,30 @@
 
 (define stars (load-sprite "stars.png" #:anchor #(0 0)))
 (define particle-image (load-texture "bullet.png"))
-(define num-particles 1800)
+(define particle-width (texture-width particle-image))
+(define particle-height (texture-height particle-image))
+(define particle-count 2000)
 (define particles
-  (list-tabulate num-particles
+  (list-tabulate particle-count
                  (lambda (n)
                    (make-particle (make-sprite particle-image)
                                   (vector (random window-width)
                                           (random window-height))
                                   (vector (* (random:normal) 1)
-                                           (* (random:normal) 1))))))
+                                          (* (random:normal) 1))))))
+(define batch (make-sprite-batch (* particle-count 4)))
+
+(define (draw-particles particles)
+  (with-sprite-batch batch
+    (for-each
+     (lambda (p)
+       (let* ((pos (particle-position p))
+              (x (vx pos))
+              (y (vy pos)))
+         (sprite-batch-draw batch particle-image x y 0 0
+                            particle-width particle-height
+                            1 1 0)))
+     particles)))
 
 (set-render-callback (lambda () (render)))
 (set-update-callback (lambda () (update)))
-- 
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