iOS OpenGLES 渲染多个对象时出现奇怪的行为

Question

我正在尝试渲染两个带有纹理（"body"和"head"）的立方体。有一个具有所有立方体面的纹理图集。为了实现这一点，我创建了一个类来封装绘制立方体的所有代码：MSTexturedCube 。

// In MSTexturedCube.h
#import <Foundation/Foundation.h>
#import <GLKit/GLKit.h>
@interface MSTexturedCube : NSObject {
    GLKVector3 _vertices[8];
    GLKVector3 _triangleVertices[36];
    GLKVector2 _textureVertices[36];
}
@property (nonatomic, assign) float xRotationAngle;
@property (nonatomic, assign) float yRotationAngle;
@property (nonatomic, assign) GLKVector3 scale;             // x, y, z scale
@property (nonatomic, assign) GLKVector3 translation;   // x, y, z translation
- (id)initWithTexture:(GLKTextureInfo *)textureInfo vertexData:(GLKVector2[36])textureVertexData;
- (id)initWithTexture:(GLKTextureInfo *)textureInfo frontFaceCoords:(GLKVector2[4])front right:(GLKVector2[4])right back:(GLKVector2[4])back left:(GLKVector2[4])left top:(GLKVector2[4])top bottom:(GLKVector2[4])bottom;
- (void)draw;
- (void)setVertices:(GLKVector3[8])verticesArray;
@end

// In MSTexturedCube.m
#import "MSTexturedCube.h"
static int vertexIndices[36] = {
    // Front
    0, 1, 2,
    0, 2, 3,
    // Right
    1, 5, 6,
    1, 6, 2,
    // Back
    5, 4, 7,
    5, 7, 6,
    // Left
    4, 0, 3,
    4, 3, 7,
    // Top
    3, 2, 6,
    3, 6, 7,
    // Bottom
    4, 5, 1,
    4, 1, 0,
};
@interface MSTexturedCube ()
@property (nonatomic, strong) GLKBaseEffect *effect;
@property (nonatomic, strong) GLKTextureInfo *textureInfo;
- (void)setupOpenGL;
@end
@implementation MSTexturedCube
@synthesize effect = _effect;
@synthesize textureInfo = _textureInfo;
@synthesize xRotationAngle = _xRotationAngle;
@synthesize yRotationAngle = _yRotationAngle;
@synthesize scale = _scale;
@synthesize translation = _translation;
// Init methods
...
- (void)draw {
    // Create matrices
    GLKMatrix4 yRotation = GLKMatrix4MakeYRotation(self.yRotationAngle);
    GLKMatrix4 xRotation = GLKMatrix4MakeXRotation(self.xRotationAngle);
    GLKMatrix4 scale = GLKMatrix4MakeScale(self.scale.x, self.scale.y, self.scale.z);
    GLKMatrix4 translation = GLKMatrix4MakeTranslation(self.translation.x, self.translation.y, self.translation.z);
    GLKMatrix4 modelMatrix = GLKMatrix4Multiply(translation, GLKMatrix4Multiply(xRotation, GLKMatrix4Multiply(yRotation, scale)));
    GLKMatrix4 viewMatrix = GLKMatrix4MakeLookAt(0.0, 0.0, 3.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
    self.effect.transform.modelviewMatrix = GLKMatrix4Multiply(viewMatrix, modelMatrix);
    self.effect.transform.projectionMatrix = GLKMatrix4MakePerspective(0.25 * M_PI, 1.0, 2.0, 500.0);
    // Set texture properties if a texture is set
    if (self.textureInfo) {
        self.effect.texture2d0.envMode = GLKTextureEnvModeReplace;
        self.effect.texture2d0.target = GLKTextureTarget2D;
        self.effect.texture2d0.name = self.textureInfo.name;
    }
    // Prepare the effect to draw after creating matrices
    [self.effect prepareToDraw];
    // Set texture
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(self.textureInfo.target, self.textureInfo.name);
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );
    // Set vertices
    glEnableVertexAttribArray(GLKVertexAttribPosition);
    glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, sizeof(float) * 3, _triangleVertices);
    // Set texture (if set)
    if (self.textureInfo) {
        glEnableVertexAttribArray(GLKVertexAttribTexCoord0);
        glVertexAttribPointer(GLKVertexAttribTexCoord0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, _textureVertices);
    }
    // Draw
    glDrawArrays(GL_TRIANGLES, 0, 36);
    // Disable arrays
    glDisableVertexAttribArray(GLKVertexAttribPosition);
    glDisableVertexAttribArray(GLKVertexAttribTexCoord0);
}
// Getters & setters
...
#pragma mark - Private methods
- (void)setupOpenGL {
    // Set vertices array
    _vertices[0] = GLKVector3Make(-0.5, -0.5,  0.5); // Left  bottom front
    _vertices[1] = GLKVector3Make( 0.5, -0.5,  0.5); // Right bottom front
    _vertices[2] = GLKVector3Make( 0.5,  0.5,  0.5); // Right top    front
    _vertices[3] = GLKVector3Make(-0.5,  0.5,  0.5); // Left  top    front
    _vertices[4] = GLKVector3Make(-0.5, -0.5, -0.5); // Left  bottom back
    _vertices[5] = GLKVector3Make( 0.5, -0.5, -0.5); // Right bottom back
    _vertices[6] = GLKVector3Make( 0.5,  0.5, -0.5); // Right top    back
    _vertices[7] = GLKVector3Make(-0.5,  0.5, -0.5); // Left  top    back
    // Set the triangle vertices
    for (int i = 0; i < 36; i++) {
        _triangleVertices[i] = _vertices[vertexIndices[i]];
    }
    self.effect = [[GLKBaseEffect alloc] init];
}

在我的GLKViewController子类中，它实现了GLKViewDelegate和GLKViewControllerDelegate，我创建了两个MSTexturedCube对象，我用必要的顶点数据和纹理顶点数据初始化它们。在GLKViewDelegate中，我编写了这个函数：

- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect {
    // Set background color
    glClearColor(0.5, 0.5, 0.5, 1.0);
    glClear(GL_COLOR_BUFFER_BIT);
    // Set properties
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_CULL_FACE);
    [self.cubes makeObjectsPerformSelector:@selector(draw)];
}

它工作得很好，但有一个问题：当我旋转视图时，cubes 数组中的第二个对象渲染没有任何问题，但第一个对象，即使它离相机更近，如果它下面有另一个对象，也会看起来绝对透明。如果它只有下面的背景，它也会渲染不透明。¿如何解决此问题，并使对象遵循 z 顺序？

Answer 1

我解决了我的问题。

我忘了通过将 GLView 的可绘制深度格式属性设置为 GLKViewDrawableDepthFormat16 来向我的EAGLContext添加深度缓冲区。

虽然它没有出现在问题中，但我试图在 GLView 的委托方法中添加以下两行，但他们什么也没做：

glDepthFunc(GL_LEQUAL);
glClear(GL_DEPTH_BUFFER_BIT);

显然，因为没有设置缓冲区。当我设置GLKViewDrawableDepthFormat16并添加这两行时，它工作得很好。