color array handling with openGL

Question

Hi guys

I am developing an ipad app with openGL. In my app basically I am drawing a basic shape i.e 3d cube, which can rotate according to user's finger motion. Now I am stuck on coloring part of this cube. I want user to choose surfaces of his choice to color this shape.

So what I am trying to do is...I am changing the array for glColorPointer() everytime when user change color. But cant got success in that. Here is the sample what I am trying to do

sample code :

const GLubyte *cubeFace1;
const GLubyte *cubeFace2;

NSMutableArray *cubeFace1Arr = [[NSMutableArray alloc] initWithCapacity:20 ];
for ( i = 0; i < 16; i++) {
// black color. value of '255' will change according to the user's selection of color
    [cubeFace1Arr addObject: [NSNumber numberWithInt:255]];
}

NSMutableArray *cubeFace2Arr = [[NSMutableArray alloc] initWithCapacity:20 ];
for ( i = 0; i < 16; i++) {
// white color. value of '0' will change according to the user's selection of color
    [cubeFace2Arr addObject: [NSNumber numberWithInt:0]];
}

cubeFace1 = cubeFace1Arr; // warning: assignment from incompatible pointer type
cubeFace1 = cubeFace2Arr; // warning: assignment from incompatible pointer type


glColorPointer(4, GL_UNSIGNED_BYTE, 0, cubeFace1);
glColorPointer(4, GL_UNSIGNED_BYTE, 0, cubeFace2);

So, my basic problem is how I generate this color array dynamically? or how I remove this waring..!!

Thanks in advance and help appreciated.

Answer 1

glColorPointer (as with most OpenGL calls) want plain C arrays, not Objective-C NSArray objects.

struct RGBAColor {
    GLubyte r, g, b, a;
};

struct RGBAColor cubeFace1[16];
for( int i = 0; i < 16; i++ ) {
    cubeFace1[i].r = 255;
    cubeFace1[i].g = 255;
    cubeFace1[i].b = 255;
    cubeFace1[i].a = 255;
}
glColorPointer( 4, GL_UNSIGNED_BYTE, 0, cubeFace1 );

I highly recommend checking out the documentation.