Initialising a C Struct Array - Objective C - OpenGLES - objective-c

Question

I have the following Vertex struct in my OpenGL ES app :
typedef struct Vertex {
float Position[3];
float Color[4];
} Vertex;
In my header I then declare :
Vertex *Vertices;
Then in my init method :
int array = 4;
Vertices = (Vertex *)malloc(array * sizeof(Vertex));
I then later setup the mesh as follows, where vertices array in this case has 4 vertices :
- (void)setupMesh {
int count = 0;
for (VerticeObject * object in verticesArray) {
Vertices[count].Position[0] = object.x;
Vertices[count].Position[1] = object.y;
Vertices[count].Position[2] = object.z;
Vertices[count].Color[0] = 0.9f;
Vertices[count].Color[1] = 0.9f;
Vertices[count].Color[2] = 0.9f;
Vertices[count].Color[3] = 1.0f;
count ++;
}
}
Can anyone spot what I am doing wrong here ? When I pass this Vertices object to OpenGL nothing is drawn, whereas if I hard code the Vertices array as :
Vertex Vertices [] = {
{{0.0, 0.0, 0}, {0.9, 0.9, 0.9, 1}},
{{0.0 , 0.0 , 0}, {0.9, 0.9, 0.9, 1}},
{{0.0, 0.0, 0}, {0.9, 0.9, 0.9, 1}},
{{0.0, 0.0, 0}, {0.9, 0.9, 0.9, 1}},
};
Everything works ?

Answer 1

I think the problem is that before you had a array allocated on the stack where now you have a pointer(memory address) to a block of memory on the heap. So when you wright stuff like sizeof(Vertices) your original sizeof(Vertices) would result in 4 vertices each holding 3 floats position and 4 floats color -> 4 * (3 + 4) * 4(float = 4 bytes) = 112 bytes. Where sizeof(aPointer) = 4 bytes. OpenGL is a C library an not super easy to work with so you should really brush up on you C skills before trying to get it running. Also there in a GLKView class now days that will make all the setup allot easier.
glBufferData(GL_ARRAY_BUFFER, sizeof(Vertices), Vertices, GL_STATIC_DRAW);
Try to allocate same size as the array of vertices. In your case 4 * sizeof(Vertex).
glBufferData(GL_ARRAY_BUFFER, sizeof(Vertex) * 4, Vertices, GL_STATIC_DRAW);
If that doesn't work you can easily fix the problem by replacing your dynamically allocated array for a statically allocated since you know at compile time how big it needs to be.
Vertex Vertices[4];
Then set the values in your loop as you do.