Software: Maya2008 COLLADA version 1. 4
COLLADA schema supports all the features that modern 3D interactive applications need, including programmable shader effects, animation and physic simulation.
Step 1.
Install and load COLLADA plug in for maya
Step 2.
Change all face of model into triangles: Mesh -> Triangulate. (OpenGL ES 1.x do not support QUADE draw).
Step 3.
Export model with mayaCollada, so I have a dae(digital asset exchange) file. In fact dae file is extended from XML file.
Step 4.
Go back to Xcode and import this .dae file into project, Open it with editor, we can find all information about 3D Model, like materials, effects, geometries… I focus my attention on tag ” library geometries” which include a sub tag “mesh”. The first line in this block define name of geometry <geometry id=”pCubeShape1″ name=”pCubeShape1″> then is the important tag <mesh>, in it there are 3 “source” and a “triangles” blocks, each of them include an array: <float_array id=”pCubeShape1-positions-array” count=”24″> (position of each vertex), <float_array id=”pCubeShape1-normals-array” count=”72″>, <source id=”pCubeShape1-map1″ name=”pCubeShape1-map1″> (texture coordinats) and <p> ( please look at to Ps). They are all what we need to a simple model to iPhone SDK import.
Step 5.
Then I can parse this file with class NSXMLParser from SDK. In this example I draw model shape without texture, so I read out only positions array and the indices array from <p>.
- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict {
if(qName) {
elementName = qName;
}
if([elementName isEqualToString:@"accessor"]) {
NSString *accessorAtt = [attributeDict valueForKey:@"source"];
if([accessorAtt isEqualToString:@"#pCubeShape1-positions-array"]) {
NSString *sVertextCount = [attributeDict valueForKey:@"count"];
vertexCount = [sVertextCount intValue];
return;
}
else if([accessorAtt isEqualToString:@"#pCubeShape1-map1-array"]) {
NSString *sMapCount = [attributeDict valueForKey:@"count"];
mapCount = [sMapCount intValue];
return;
}
}
else if([elementName isEqualToString:@"triangles"]) {
NSString *sFaceCount = [attributeDict valueForKey:@"count"];
faceCount = [sFaceCount intValue];
return;
}
else if ([elementName isEqualToString:@"float_array"]) {
NSString *relAtt = [attributeDict valueForKey:@"id"];
if([relAtt isEqualToString:@"pCubeShape1-positions-array"]) {
contentProperty = [NSMutableString string];
array_id = id_positions;
NSLog(@”get positions”);
}
else if([relAtt isEqualToString:@"pCubeShape1-normals-array"]) {
contentProperty = [NSMutableString string];
array_id = id_normals;
NSLog(@”get normals”);
}
else if([relAtt isEqualToString:@"pCubeShape1-map1-array"]) {
contentProperty = [NSMutableString string];
array_id = id_maps;
NSLog(@”get maps”);
}
}
else if ([elementName isEqualToString:@"p"]) {
contentProperty = [NSMutableString string];
NSLog(@”get vertex”);
}
else {
contentProperty = nil;
}
}
- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName
{
if (qName) {
elementName = qName;
}
if ([elementName isEqualToString:@"float_array"]) {
if(array_id == id_positions) {
msd.sPosition = contentProperty;
NSLog(@”set postion”);
array_id = -1;
}
if(array_id == id_normals) {
msd.sNormal = contentProperty;
NSLog(@”set normals”);
array_id = -1;
}
if(array_id == id_maps) {
msd.sMap = contentProperty;
NSLog(@”set maps”);
array_id = -1;
}
}
else if ([elementName isEqualToString:@"p"]) {
msd.sIndices = contentProperty;
NSLog(@”set vertex”);
}
}
- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string
{
if (contentProperty) {
[contentProperty appendString:string];
}
}
Step 6.
At last we can draw our model with OpenGL ES.
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, mVertices);
glDrawArrays(GL_TRIANGLES, 0, faceCount*3);
glDisableClientState(GL_VERTEX_ARRAY);
Ps:
The <p> contains indices that describe the vertex attributes for a number of triangles. The indices in a <p> element refer to different inputs depending on their order. The first index in a <p> element refers to all inputs with an offset of 0. The second index refers to all inputs with an offset of 1.
Each vertex of the triangle is made up of one index into each input. After each input is used, the next index again refers to the inputs with offset of 0 and begins a new vertex.
The winding order of vertices produced is counterclockwise and describes the front side of each triangle.
If the primitives are assembled without vertex normals then the application may generate per-primitive
normals to enable lighting.
Here is an example of a <triangles> element that describes two triangles. There are two <source> elements that contain the position and normal data, according to the <input> element semantics. The <p> element index values indicate the order in which the input values are used:
<mesh>
<source id=”position”/>
<source id=”normal”/>
<vertices id=”verts”>
<input semantic=”POSITION” source=”#position”/>
</vertices>
<triangles count=”2″ material=”Bricks”>
<input semantic=”VERTEX” source=”#verts” offset=”0″/>
<input semantic=”NORMAL” source=”#normal” offset=”1″/>
<p>
0 0 1 3 2 1
0 0 2 1 3 2
</p>
</triangles>
</mesh>
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