一、SCNScene系统API导出STL格式模型会出现细节丢失问题
- (BOOL)writeToURL:(NSURL *)url options:(nullable NSDictionary<NSString *, id> *)options delegate:(nullable id <SCNSceneExportDelegate>)delegate progressHandler:(nullable SCNSceneExportProgressHandler)progressHandler;
二、STL文件格式：二进制格式
起始有80个字节文件头用于存储文件名，接着4个字节表示三角面片的数量【数量一定要正确，否则导出的模型会显示异常】，每个三角面片占用固定的50个字节：法向矢量---3个4字节浮点数、三角面的三个顶点：每个顶点为3个4字节浮点数，接着是2个字节描述三角形基本属性【暂时没有用到】
三、实现
/// 保存多个模型到一个文件：异步操作
/// @param nodes 模型节点列表
/// @param filePath <#filePath description#>
/// @param complete <#complete description#>
+(void)xlSaveSCNNodes:(NSArray *)nodes
toFile:(NSString *)filePath
complete:(void(^)(NSError *error))complete{
dispatch_async(dispatch_get_global_queue(0, 0), ^{
// 写文件句柄
NSFileHandle *fileHandler = [self xlFileHandleForWritingAtPath:filePath];
// 写入文件头
NSError *error = nil;
NSString *name = filePath.lastPathComponent;
name = [name stringByDeletingPathExtension];
NSData *data = [name dataUsingEncoding:NSUTF8StringEncoding];
if (data.length > 80) {
data = [data subdataWithRange:NSMakeRange(0, 80)];
[self xlFileHandler:fileHandler writeData:data error:&error];
} else {
[self xlFileHandler:fileHandler writeData:data error:&error];
NSInteger datCcount = 80 - data.length;
NSString *space = @"";
for (int index = 0; index < datCcount; index ++) {
space = [space stringByAppendingString:@" "];
}
data = [space dataUsingEncoding:NSUTF8StringEncoding];
[self xlFileHandler:fileHandler writeData:data error:&error];
}
// 写入面的个数
NSInteger allCount = [self xlNormalsWithNodes:nodes];
data = [NSData dataWithBytes:&allCount length:sizeof(int)];
[self xlFileHandler:fileHandler writeData:data error:&error];
// 保存法线与顶点信息
for (SCNNode *node in nodes) {
SCNGeometry *geometry = node.geometry;
// 法线信息
NSArray<SCNGeometrySource *> *normals = [geometry geometrySourcesForSemantic:SCNGeometrySourceSemanticNormal];
SCNGeometrySource *normal = normals[0];
// 顶点信息
NSArray<SCNGeometrySource *> *vertices = [geometry geometrySourcesForSemantic:SCNGeometrySourceSemanticVertex];
SCNGeometrySource *vertice = vertices[0];
NSInteger normalCount = (normal.data.length - normal.dataOffset) / normal.dataStride / 3;
NSMutableData *mData = [NSMutableData data];
char a[2];
NSData *vectorData = nil;
SCNMatrix4 matrix4 = node.worldTransform;
GLKMatrix4 glkMatrix4 = SCNMatrix4ToGLKMatrix4(matrix4);
for (int i = 0; i < normalCount; i ++) {
NSData *data = [normal.data subdataWithRange:NSMakeRange(normal.dataOffset + i * normal.dataStride * 3, normal.dataStride)];
SCNVector3 nVector3 = [self xlVector3FromData:data];
vectorData = [NSData dataWithBytes:&(nVector3.x) length:4];
[mData appendData:vectorData];
vectorData = [NSData dataWithBytes:&(nVector3.y) length:4];
[mData appendData:vectorData];
vectorData = [NSData dataWithBytes:&(nVector3.z) length:4];
[mData appendData:vectorData];
for (int j = 0; j <= 2; j ++) {
data = [vertice.data subdataWithRange:NSMakeRange(i * normal.dataStride * 3 + j*normal.dataStride, normal.dataStride)];
nVector3 = [self xlVector3FromData:data];
GLKVector3 glkVector3 = SCNVector3ToGLKVector3(nVector3);
GLKVector3 nGLKVector3 = GLKMatrix4MultiplyAndProjectVector3(glkMatrix4, glkVector3);
nVector3 = SCNVector3FromGLKVector3(nGLKVector3);
vectorData = [NSData dataWithBytes:&(nVector3.x) length:4];
[mData appendData:vectorData];
vectorData = [NSData dataWithBytes:&(nVector3.y) length:4];
[mData appendData:vectorData];
vectorData = [NSData dataWithBytes:&(nVector3.z) length:4];
[mData appendData:vectorData];
}
[mData appendBytes:(char*)(a) length:sizeof(char) * 2];
}
[self xlFileHandler:fileHandler writeData:mData error:&error];
}
if (@available(iOS 13.0, *)) {
NSError *closeError = nil;
[fileHandler closeAndReturnError:&closeError];
if (complete) {
dispatch_async(dispatch_get_main_queue(), ^{
complete(nil);
});
}
} else {
[fileHandler closeFile];
if (complete) {
dispatch_async(dispatch_get_main_queue(), ^{
complete(nil);
});
}
}
});
}
// 计算面个数
+(NSInteger)xlNormalsWithNodes:(NSArray *)nodes{
NSInteger allCount = 0;
for (SCNNode *node in nodes) {
SCNGeometry *geometry = node.geometry;
// 获取法线信息
NSArray<SCNGeometrySource *> *normals = [geometry geometrySourcesForSemantic:SCNGeometrySourceSemanticNormal];
// 获取法线信息
SCNGeometrySource *normal = normals[0];
allCount = allCount + (normal.data.length - normal.dataOffset) / normal.dataStride / 3;
}
return allCount;
}
// 文件句柄
+(NSFileHandle *)xlFileHandleForWritingAtPath:(NSString *)filePath{
NSFileHandle *fileHandler = [NSFileHandle fileHandleForWritingAtPath:filePath];
if(fileHandler == nil) {
[[NSFileManager defaultManager] createFileAtPath:filePath contents:nil attributes:nil];
fileHandler = [NSFileHandle fileHandleForWritingAtPath:filePath];
}
return fileHandler;
}
// NSData转坐标
+(SCNVector3)xlVector3FromData:(NSData *)data{
float tmpValue[1];
float v0, v1, v2;
NSData *tmpData = [data subdataWithRange:NSMakeRange(0, 4)];
[tmpData getBytes:tmpValue length:4];
v0 = tmpValue[0];
tmpData = [data subdataWithRange:NSMakeRange(4, 4)];
[tmpData getBytes:tmpValue length:4];
v1 = tmpValue[0];
tmpData = [data subdataWithRange:NSMakeRange(4 * 2, 4)];
[tmpData getBytes:tmpValue length:4];
v2 = tmpValue[0];
return SCNVector3Make(v0, v1, v2);
}
// SCN坐标系转OpenGL坐标系
+(SCNVector3)xlSCNMatrix4:(SCNMatrix4)scnMatrix4 multiplyAndProjectVector3:(SCNVector3)scnVector3{
GLKMatrix4 glkMatrix4 = SCNMatrix4ToGLKMatrix4(scnMatrix4);
GLKVector3 glkVector3 = SCNVector3ToGLKVector3(scnVector3);
GLKVector3 nGLKVector3 = GLKMatrix4MultiplyAndProjectVector3(glkMatrix4, glkVector3);
return SCNVector3FromGLKVector3(nGLKVector3);
}
// 写文件
+(void)xlFileHandler:(NSFileHandle *)fileHandler writeData:(NSData *)data error:(NSError **)error{
if (@available(iOS 13.0, *)) {
[fileHandler writeData:data error:error];
} else {
// Fallback on earlier versions
[fileHandler writeData:data];
}
}
四、其他
ASCII编码格式的STL文件导出未实现，可以参考STL文件解析来处理ASCII编码格式的STL文件导出。
函数中计算法向量数使用的normal.dataOffset，为数据的起始偏移值，不同的加载方式该值可能不同【暂时遇到过0、12】，normal.dataStride为单个顶点数据的字节长度。
刚接触3D渲染框架，难免有错漏，欢迎评论留言指出。
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