From af06cc8002215c50cc07f4a40b643d3b1978450f Mon Sep 17 00:00:00 2001
From: Matt Turner <mattst88@gmail.com>
Date: Wed, 24 Oct 2012 21:29:35 -0700
Subject: Use instanced rendering

Note: calling glDrawElementsInstanced (non-ARB) causes a segfault.
---
 data/instanced.vert | 13 +++++++++++++
 src/main.cpp        | 49 ++++++++++++++++++++++++++++++++++++++++---------
 2 files changed, 53 insertions(+), 9 deletions(-)
 create mode 100644 data/instanced.vert

diff --git a/data/instanced.vert b/data/instanced.vert
new file mode 100644
index 0000000..52a9713
--- /dev/null
+++ b/data/instanced.vert
@@ -0,0 +1,13 @@
+#extension GL_ARB_draw_instanced : enable
+
+uniform mat4 mvp[5];
+
+attribute vec4 vert_color;
+
+varying vec4 color;
+
+void main(void)
+{
+	gl_Position = mvp[gl_InstanceID] * gl_Vertex;
+	color = abs(vert_color);
+}
diff --git a/src/main.cpp b/src/main.cpp
index 7ead051..200cd89 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -35,6 +35,7 @@ static SDL_Surface *my_surf = NULL;
 
 static bool anim = true;
 static bool done = false;
+static bool instanced = false;
 
 static float y_angle = 0.0f;
 static float hinge_angle = 0.0f;
@@ -237,20 +238,36 @@ Redisplay(void)
 	if (timer_queries[0])
 		glBeginQuery(GL_TIME_ELAPSED, timer_queries[0]);
 
-	for (unsigned i = 0; i < ARRAY_SIZE(transformations); i++) {
+	if (instanced) {
 		/* Set the modelview-projection matrix for rendering this
 		 * object.
 		 */
-		glUniformMatrix4fv(cube_program->mvp_uniform, 1, false,
-				   (float *) &transformations[i]);
+		glUniformMatrix4fv(cube_program->mvp_uniform, ARRAY_SIZE(transformations), false,
+				   (float *) &transformations[0]);
 
 
 		/* Draw the object.
 		 */
-		glDrawElements(cube_sink->mode,
-			       cube_sink->elt_count,
-			       GL_UNSIGNED_SHORT,
-			       BUFFER_OFFSET(cube_sink->elt_offset));
+		glDrawElementsInstancedARB(cube_sink->mode,
+					   cube_sink->elt_count,
+					   GL_UNSIGNED_SHORT,
+					   BUFFER_OFFSET(cube_sink->elt_offset),
+					   ARRAY_SIZE(transformations));
+	} else {
+		for (unsigned i = 0; i < ARRAY_SIZE(transformations); i++) {
+			/* Set the modelview-projection matrix for rendering this
+			 * object.
+			 */
+			glUniformMatrix4fv(cube_program->mvp_uniform, 1, false,
+					   (float *) &transformations[i]);
+
+			/* Draw the object.
+			 */
+			glDrawElements(cube_sink->mode,
+				       cube_sink->elt_count,
+				       GL_UNSIGNED_SHORT,
+				       BUFFER_OFFSET(cube_sink->elt_offset));
+		}
 	}
 
 	if (timer_queries[0])
@@ -368,8 +385,14 @@ build_all_shaders(void)
 
 	/* Compile all of the shaders
 	 */
-	GLuint vs = compile_shader_from_file(GL_VERTEX_SHADER,
-					     "simple.vert");
+	GLuint vs;
+	if (instanced) {
+		vs = compile_shader_from_file(GL_VERTEX_SHADER,
+					      "instanced.vert");
+	} else {
+		vs = compile_shader_from_file(GL_VERTEX_SHADER,
+					      "simple.vert");
+	}
 	GLuint fs = compile_shader_from_file(GL_FRAGMENT_SHADER,
 					     "simple.frag");
 
@@ -421,6 +444,7 @@ Init(void)
 	       "    f: Toggle fullscreen.\n"
 	       "    a: Toggle animation of object.\n"
 	       "    c: Re-load and compile shader program code.\n"
+	       "    i: Toggle instanced rendering.\n"
 	       "  ESC: Exit program.\n");
 }
 
@@ -469,6 +493,13 @@ Key(SDLKey sym, bool key_down)
 		build_all_shaders();
 		break;
 
+	case 'i':
+		instanced = !instanced;
+		build_all_shaders();
+		printf("Using %sinstanced rendering.\n",
+		       instanced ? "" : "non-");
+		break;
+
 	default:
 		break;
 	}
-- 
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