From 5c9edba75c934dae9d11ae0998b92c789db3a920 Mon Sep 17 00:00:00 2001
From: Luke Lau <luke_lau@icloud.com>
Date: Sun, 16 Sep 2018 13:26:10 +0100
Subject: [PATCH 1/1] Draw 2 triangles with 2 VAOS+VBOS

---
 assignment1.cpp | 64 +++++++++++++++++++++++++++----------------------
 1 file changed, 36 insertions(+), 28 deletions(-)

diff --git a/assignment1.cpp b/assignment1.cpp
index 43cd626..fd55f4e 100644
--- a/assignment1.cpp
+++ b/assignment1.cpp
@@ -13,9 +13,14 @@
 
 using namespace std;
 
+GLuint* vaos;
+
 void display() {
 	glClear(GL_COLOR_BUFFER_BIT);
-	glDrawArrays(GL_TRIANGLES, 0, 6);
+	for (int i = 0; i < 2; i++) {
+		glBindVertexArray(vaos[i]);
+		glDrawArrays(GL_TRIANGLES, 0, 3);
+	}
 	glutSwapBuffers();
 }
 
@@ -65,63 +70,66 @@ GLuint compileShaders() {
 	return progId;
 }
 
-void generateObjectBuffers() {
-	GLfloat vertices[] = {
+#define BUFFER_OFFSET(i) ((char *)NULL + (i))
+
+GLuint* setupBuffers(GLuint progId) {
+	GLfloat vertices[2][9] = {
+		{
 			0.0f, -1.0f, 0.0f,
 			1.0f, -1.0f, 0.0f,
-		0.5f, 1.0f, 0.0f,
+			0.5f, 1.0f, 0.0f
+		},
 
+		{
 			-1.0f, -1.0f, 0.0f,
 			0.0f, -1.0f, 0.0f,
 			-0.5f, 1.0f, 0.0f
+		}
 	};
 
 	GLfloat colors[] = {
-		0, 1, 0, 1,
-		1, 0, 0, 1,
-		0, 0, 1, 1,
-		
 		0, 1, 0, 1,
 		1, 0, 0, 1,
 		0, 0, 1, 1
 	};
 
-	GLuint numVerts = 6;
+	GLuint numVerts = 3;
+
+	GLuint vbos[2];
+	glGenBuffers(2, vbos);
 
-	GLuint VBO;
-	glGenBuffers(1, &VBO);
-	glBindBuffer(GL_ARRAY_BUFFER, VBO);
-	glBufferData(GL_ARRAY_BUFFER, numVerts * 7 * sizeof(GLfloat), NULL, GL_STATIC_DRAW);
+	GLuint* vaos = new GLuint[2];
+	glGenVertexArrays(2, vaos);
+
+	GLuint posId = glGetAttribLocation(progId, "vPosition");
+	GLuint colorId = glGetAttribLocation(progId, "vColor");
 
 	GLuint vertsLen = numVerts * 3 * sizeof(GLfloat);
 	GLuint colorsLen = numVerts * 4 * sizeof(GLfloat);
-	glBufferSubData(GL_ARRAY_BUFFER, 0, vertsLen, vertices);
-	glBufferSubData(GL_ARRAY_BUFFER, vertsLen, colorsLen, colors);
-}
 
-#define BUFFER_OFFSET(i) ((char *)NULL + (i))
 
-void linkBuffers(GLuint progId) {
-	GLuint numVerts = 6;
-	GLuint posId = glGetAttribLocation(progId, "vPosition");
-	GLuint colorId = glGetAttribLocation(progId, "vColor");
+	for(int i = 0; i < 2; i++) {
+		glBindBuffer(GL_ARRAY_BUFFER, vbos[i]);
+		glBufferData(GL_ARRAY_BUFFER, vertsLen + colorsLen, NULL, GL_STATIC_DRAW);
+
+		glBufferSubData(GL_ARRAY_BUFFER, 0, vertsLen, vertices[i]);
+		glBufferSubData(GL_ARRAY_BUFFER, vertsLen, colorsLen, colors);
 		
-	GLuint vao = 0;
-	glGenVertexArrays(1, &vao);
-	glBindVertexArray(vao);
+		glBindVertexArray(vaos[i]);
 
 		glEnableVertexAttribArray(posId);
-	glVertexAttribPointer(posId, 3, GL_FLOAT, GL_FALSE, 0, 0);
-
 		glEnableVertexAttribArray(colorId);
+		
+		glVertexAttribPointer(posId, 3, GL_FLOAT, GL_FALSE, 0, 0);
 		glVertexAttribPointer(colorId, 4, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(numVerts * 3 * sizeof(GLfloat)));
+	}
 
+	return vaos;
 }
 
 void init() {
 	GLuint progId = compileShaders();
-	generateObjectBuffers();
-	linkBuffers(progId);
+	vaos = setupBuffers(progId);
 	
 	glValidateProgram(progId);
 	
-- 
2.30.2