Sharing Struct Information Between Classes - Objective C - OpenGL ES - iphone

Question

I have an OpenGL ES based app with the following structure :
I parse vertices from a DAE file which contains a number of objects (using NSXMLParser).
As I parse each set of vertices, I create an object (sceneObject) and set the vertices array in this object to match the parsed vertices. I am then planning to add these sceneObjects to array of objects to be rendered by OpenGL ES.
Initially I had taken an approach of using NSArrays to store the vertice data, however I understand that the OpenGL commands (such as glvertexpointer) do not accept NSObject values, bue instead need raw values (glfloats and gluints etc).
Rather than convert the NSObjects back to GL raw values within the object class, I am now trying to take a struct approach. This is the code where I parse the vertice information :
if (floatArray) {
if (currentlyParsing == kVerticeInformation) {
if (currentParserTagType == kGeometry) {
//NSLog(#"Loaded Vertices %#", string);
NSArray * nums = [string componentsSeparatedByString:#" "];
culmunativeCount += [nums count];
//NSLog(#"Culm Count is %d", culmunativeCount);
[fullParseString appendString : string];
if (checkSumCount <= culmunativeCount) {
//NSLog(#"Full Parse String is %#", fullParseString);
NSArray * finishedArray = [fullParseString componentsSeparatedByString:#" "];
//NSLog(#"Finihsed ARray is %d", [finishedArray count]);
[finishedParsingArray addObjectsFromArray:finishedArray];
//NSLog(#" FINISHED PARSING = %d", [finishedParsingArray count]);
NSUInteger baseIndex;
for (baseIndex=0; baseIndex <[finishedParsingArray count]; baseIndex +=3) {
NSString * xPoint = [finishedParsingArray objectAtIndex:baseIndex];
NSDecimalNumber * errorCheckX = [NSDecimalNumber decimalNumberWithString:xPoint];
float x = [errorCheckX floatValue];
NSString * yPoint = [finishedParsingArray objectAtIndex:baseIndex +1];
NSDecimalNumber * errorCheckY = [NSDecimalNumber decimalNumberWithString:yPoint];
float y = [errorCheckY floatValue];
NSString * zPoint = [finishedParsingArray objectAtIndex:baseIndex+2];
NSDecimalNumber * errorCheckZ = [NSDecimalNumber decimalNumberWithString:zPoint];
float z = [errorCheckZ floatValue];
Vertex3D vertexItem = {x,y,z}
//NSLog(#"Vertices stored are %f, %f, %f", x,y,z);
}
currentlyParsing = kNilSetting;
checkSumCount = 0;
[finishedParsingArray removeAllObjects];
//[finishedArray release];
culmunativeCount = 0;
[fullParseString setString:#""];
}
}
}
}
As you can see, I am now creating a Vertex3D C Struct each time with the parsed vertice information.
My questions are :
How would I then create an array of these individual C Vertex3D structs ?
How can I then pass this array of structs to my sceneObject ?

Answer 1

Create Objective C wrapper class for your array. It can hold several arrays (e.g. vertices, normals and tangents). You know the array size beforehand, so you can preallocate the required amount of space:
#interface MYVertexArray : NSObject {
float* _mVerts;
float* _mNormals;
int _mCount;
}
#property(nonatomic, readonly) float* verts;
#property(nonatomic, readonly) float* norms;
/**
Here you're allocating your arrays (don't forget to free them is dealloc).
*/
-(id) initWithSize:(int) size;
#end
and then in cycle, you're just doing this:
MYVertexArray* my_vertex_data = [[MYVertexArray alloc] initWithSize: [finishedParsingArray count]];
for(int i=0; i<[finishedParsingArray count]; ++i) {
my_vertex_data.verts[i] = [[finishedParsingArray objectAtIndex: i] floatValue];
}