iOS+SceneKit：如何在纹理上应用卡通着色器？

Question

我想在 iOS8+ 上使用带有 SceneKit 的卡通着色器来渲染一个带有地球纹理的球体。我还想添加一个卡通着色器来渲染地球。到目前为止，着色器在光照上工作，但纹理没有被卡通着色器着色（参见下图，纹理也应该是“卡通”的）。

有人有什么想法吗？

这是我的视图控制器代码（self.sceneKitView 是 SCNView 的一个实例）：

@implementation ToonViewController

- (void)viewDidLoad {

    [super viewDidLoad];

    SCNScene *scene = [SCNScene scene];

    // create and add a camera to the scene
    SCNNode *cameraNode = [SCNNode node];
    cameraNode.camera = [SCNCamera camera];
    [scene.rootNode addChildNode:cameraNode];
    // place the camera
    cameraNode.position = SCNVector3Make(0, 0, 15);

    // create and add a light to the scene
    SCNNode *lightNode = [SCNNode node];
    lightNode.light = [SCNLight light];
    lightNode.light.type = SCNLightTypeOmni;
    lightNode.position = SCNVector3Make(0, 10, 10);
    [scene.rootNode addChildNode:lightNode];

    // create and add an ambient light to the scene
    SCNNode *ambientLightNode = [SCNNode node];
    ambientLightNode.light = [SCNLight light];
    ambientLightNode.light.type = SCNLightTypeAmbient;
    ambientLightNode.light.color = [UIColor darkGrayColor];
    [scene.rootNode addChildNode:ambientLightNode];

    // set up the scene
    self.sceneKitView.scene = scene;
    self.sceneKitView.allowsCameraControl = YES;
    self.sceneKitView.showsStatistics = NO;
    self.sceneKitView.backgroundColor = [UIColor clearColor];

    NSMutableDictionary* shaders = [[NSMutableDictionary alloc] init];
    shaders[SCNShaderModifierEntryPointLightingModel] = [[NSString alloc] initWithContentsOfURL:[[NSBundle mainBundle] URLForResource:@"fixed_toon" withExtension:@"shader"]
                                                                                       encoding:NSUTF8StringEncoding
                                                                                          error:nil];

    SCNNode* earth = [SCNNode nodeWithGeometry:[SCNSphere sphereWithRadius:5.0]];
    earth.position = SCNVector3Make(0.0, 0.0, 0.0);
    [scene.rootNode addChildNode:earth];

    [earth runAction:[SCNAction repeatActionForever:[SCNAction rotateByX:0.0 y:0.25 z:0.0 duration:1.0]]];

    SCNMaterial* earthMaterial = [SCNMaterial material];
    earthMaterial.diffuse.contents = [UIImage imageNamed:@"Earth.png"];
    earthMaterial.specular.contents = [UIColor whiteColor];
    earthMaterial.specular.intensity = 0.2;
    earthMaterial.locksAmbientWithDiffuse = NO;
    earthMaterial.shaderModifiers = shaders;

    earth.geometry.firstMaterial = earthMaterial;

}

@end

这是 fixed_toon.shader 文件：

vec3 lDir = normalize(vec3(0.1, 1.0, 1.0));
float dotProduct = dot(_surface.normal, lDir);

_lightingContribution.diffuse += (dotProduct*dotProduct*_light.intensity.rgb);
_lightingContribution.diffuse = floor(_lightingContribution.diffuse*4.0)/3.0;

vec3 halfVector = normalize(lDir + _surface.view);

dotProduct = max(0.0, pow(max(0.0, dot(_surface.normal, halfVector)), _surface.shininess));
dotProduct = floor(dotProduct*3.0)/3.0;

//_lightingContribution.specular += (dotProduct*_light.intensity.rgb);
_lightingContribution.specular = vec3(0,0,0);

Answer 1

您拥有的着色器只是一个光照着色器。如果你想让地球被染色，你需要一个片段着色器。

查看着色器文件，所有的数学运算都与光有关。您需要一些可以调整纹理像素颜色的东西。然后使用 SCNShaderModifierEntryPointFragment 入口点连接它。