Add colour attribute to triangle vertices

shaders/frag.glsl

@@ -1,7 +1,8 @@
 #version 460 core
 
+in vec3 vert_colours;
 out vec4 color;
 
 void main() {
-  color = vec4(0.93f, 0.42f, 0.35f, 1.0f);
+  color = vec4(vert_colours.r, vert_colours.g, vert_colours.b, 1.0f);
 };

shaders/vert.glsl

@@ -1,7 +1,11 @@
 #version 460 core
 
-in vec4 position;
+layout(location=0) in vec3 position;
+layout(location=1) in vec3 vert_colour;
+
+out vec3 vert_colours;
 
 void main() {
-  gl_Position = vec4(position.x, position.y, position.z, position.w);
+  vert_colours = vert_colour;
+  gl_Position = vec4(position.x, position.y, position.z, 1.0f);
 };

src/main.cc

@@ -115,8 +115,11 @@ int init(App &app) {
 void create_vertex_spec(App &app) {
   const std::vector<GLfloat> vertices = {
     -0.8f, -0.8f, 0.0f, // position
+     1.0f,  0.0f, 0.0f, // colour
      0.8f, -0.8f, 0.0f, // position
+     0.0f,  1.0f, 0.0f, // colour
      0.0f,  0.8f, 0.0f, // position
+     0.0f,  0.0f, 1.0f, // colour
   };
 
   // Create and activate the VAO
@@ -131,13 +134,19 @@ void create_vertex_spec(App &app) {
                GL_STATIC_DRAW
   );
 
+  GLsizei vertex_stride          = 6 * sizeof(GLfloat);
+  GLvoid  *position_start_offset = (void *)0;
+  GLvoid  *colour_start_offset   = (void *)(3 * sizeof(GLfloat));
+
   // Defines the vertex attributes and their indices. This defines the attribute for the currently
   // bound VAO
   glEnableVertexAttribArray(0);
+  glEnableVertexAttribArray(1);
 
   // Defines the number of components for the attribute, its type, the stride between the component
   // for each vertex and the offset of the first instance of the component in the buffer
-  glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void *)0);
+  glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, vertex_stride, position_start_offset);
+  glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, vertex_stride, colour_start_offset);
 
   // Cleanup.
   // The order matters. Unbind VAO first then disable the attributes. If you do it the
@@ -146,6 +155,7 @@ void create_vertex_spec(App &app) {
   glBindVertexArray(0);
   glBindBuffer(GL_ARRAY_BUFFER, 0);
   glDisableVertexAttribArray(0);
+  glDisableVertexAttribArray(1);
 }
 
 void create_graphics_pipeline(App &app) {