From c3e0f81a2881983d289a08ccda03683fb7d3137a Mon Sep 17 00:00:00 2001
From: Ravenwater <theo@stillwater-sc.com>
Date: Thu, 2 Jan 2025 09:36:03 -0500
Subject: [PATCH] WIP: refactoring vertex info into separate position and color
 attributes

---
 src/shaders/fragment.glsl |  3 +--
 src/shaders/vertex.glsl   | 13 +++++++++----
 src/triangle_mesh.cpp     | 37 +++++++++++++++++++++++++------------
 src/triangle_mesh.hpp     |  8 ++++++--
 4 files changed, 41 insertions(+), 20 deletions(-)

diff --git a/src/shaders/fragment.glsl b/src/shaders/fragment.glsl
index d4d30c7..bb6e3ce 100644
--- a/src/shaders/fragment.glsl
+++ b/src/shaders/fragment.glsl
@@ -4,7 +4,6 @@ in vec3 fragmentColor;
 
 out vec4 screenColor;
 
-void main()
-{
+void main() {
     screenColor = vec4(fragmentColor, 1.0);
 }
\ No newline at end of file
diff --git a/src/shaders/vertex.glsl b/src/shaders/vertex.glsl
index e9580e5..b4679d8 100644
--- a/src/shaders/vertex.glsl
+++ b/src/shaders/vertex.glsl
@@ -1,12 +1,17 @@
 #version 330 core
 
 layout (location=0) in vec3 vertexPos;
-layout (location=1) in vec3 vertexColor;
+layout (location=1) in int colorIndex;
 
 out vec3 fragmentColor;
 
-void main()
-{
+const vec3 colors[3] = vec3[](
+	vec3(1.0, 0.0, 0.0),
+	vec3(0.0, 1.0, 0.0),
+	vec3(0.0, 0.0, 1.0)
+);
+
+void main() {
     gl_Position = vec4(vertexPos, 1.0);
-    fragmentColor = vertexColor;
+    fragmentColor = colors[colorIndex];
 }
\ No newline at end of file
diff --git a/src/triangle_mesh.cpp b/src/triangle_mesh.cpp
index 999a9a4..c5ee495 100644
--- a/src/triangle_mesh.cpp
+++ b/src/triangle_mesh.cpp
@@ -4,30 +4,43 @@
 #include "triangle_mesh.hpp"
 
 TriangleMesh::TriangleMesh() {
+    vertex_count = 3;
+
+    std::vector<float> positions = {
+         -1.0f, -1.0f, 0.0f,
+          1.0f, -1.0f, 0.0f,
+         -1.0f,  1.0f, 0.0f
+    };
     
-    std::vector<float> data = {
-        -0.5f, -0.5f, 0.0f, 1.0f, 0.0f, 0.0f,
-         0.5f, -0.5f, 0.0f, 0.0f, 1.0f, 0.0f,
-         0.0f,  0.5f, 0.0f, 0.0f, 0.0f, 1.0f
+    std::vector<int> colorIndices = {
+		0, 1, 2
     };
-    vertex_count = 3;
 
     glGenVertexArrays(1, &VAO);
     glBindVertexArray(VAO);
 
-    glGenBuffers(1, &VBO);
-    glBindBuffer(GL_ARRAY_BUFFER, VBO);
-    glBufferData(GL_ARRAY_BUFFER, data.size() * sizeof(float), data.data(), GL_STATIC_DRAW);
+    // Vertex Buffer objects
+    VBO.resize(2);
+    glGenBuffers(2, VBO.data());
 
     // position
-    // vertexAttribPointer(index, size, type, normalized, stride, pointer)
-    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 24, (void*)0);
+    glBindBuffer(GL_ARRAY_BUFFER, VBO[0]);
+    glBufferData(GL_ARRAY_BUFFER, positions.size() * sizeof(float), positions.data(), GL_STATIC_DRAW);
+  // vertexAttribPointer(index, size, type, normalized, stride, pointer)
+    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 12 /* stride to next attribute */, (void*)0);
     glEnableVertexAttribArray(0);
 
     // color
-    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 24, (void*)12);
+    glBindBuffer(GL_ARRAY_BUFFER, VBO[1]);
+    glBufferData(GL_ARRAY_BUFFER, colorIndices.size() * sizeof(int), colorIndices.data(), GL_STATIC_DRAW);
+    // vertexAttribIPointer(index, size, type, stride, pointer)
+    glVertexAttribIPointer(1, 1, GL_INT, 4 /* stride to next attribute */, (void*)0);  // <---- notice the attrib integer pointer function signature
     glEnableVertexAttribArray(1);
 
+	// the VBO handles are stored in the VAO
+	// and the specific VBO, that is VBO[0] and VBO[1] are tied to the location 0 and 1 of the vertex shader
+    // location=0 is glVertexAttribPointer( -->0<--...
+    // location=1 is glVertexAttribIPointer( -->1<--...
 }
 
 void TriangleMesh::draw() {
@@ -37,5 +50,5 @@ void TriangleMesh::draw() {
 
 TriangleMesh::~TriangleMesh() {
     glDeleteVertexArrays(1, &VAO);
-    glDeleteBuffers(1, &VBO);
+    glDeleteBuffers(2, VBO.data());
 }
\ No newline at end of file
diff --git a/src/triangle_mesh.hpp b/src/triangle_mesh.hpp
index 31f0b3f..06bc622 100644
--- a/src/triangle_mesh.hpp
+++ b/src/triangle_mesh.hpp
@@ -1,3 +1,4 @@
+#include <vector>
 
 class TriangleMesh {
 public:
@@ -8,7 +9,10 @@ class TriangleMesh {
 
 private:
 	unsigned int vertex_count;
-	unsigned int VBO;  // VBO - Vertex Buffer Object
-	unsigned int VAO;  // VAO - Vertex Array Object
 
+	// VAO - Vertex Array Object
+	unsigned int VAO;  
+	
+	// VBO - Vertex Buffer Objects
+	std::vector<unsigned int> VBO;
 };
\ No newline at end of file