Question

我正在尝试在iOS上学习OpenGL。我正在学习本教程。

http://www.raywenderlich.com/5235/beginning-opengl-es-2-0-with-glkit-part-2

我确定我会仔细按照步骤操作，但是当我走到尽头时，屏幕上看不到任何形状。

https://gist.github.com/seanhess/5356598

我确实看到背景颜色发生了变化，因此OpenGL正在发挥作用。只是对glDrawElements的调用似乎没有做任何事情。

glDrawElements(GL_TRIANGLES, sizeof(Indices)/sizeof(Indices[0]), GL_UNSIGNED_BYTE, 0);

他有一些演示代码，但它与你在教程中编写的代码不同，我想了解为什么在粘贴之前它不起作用。

应该绘制GLKBaseEffect的位置？我看不出我们是如何使用它的。

Answer 1

以下似乎是错误的，因为所有顶点都是相同的：

// these are not TRIANGLES, they are vertices
const Vertex Vertices[]  = {
    {{1, -1, 0}, {1, 0, 0, 1}},
    {{1, -1, 0}, {1, 0, 0, 1}},
    {{1, -1, 0}, {1, 0, 0, 1}},
    {{1, -1, 0}, {1, 0, 0, 1}},
};

即使其他一切都是正确的，你的三角形也会退化为所有顶点都是重合的。当你修复坐标时，make 确保索引以逆时针方式引用顶点时尚，或者，对于您的第一次实验更好，请致电

glDisable(GL_CULL_FACE);

在绘图之前

您可以尝试选择这样的顶点：

// these are not TRIANGLES, they are vertices
const Vertex Vertices[]  = {
    {{-.9, -.9, 0}, {1, 0, 0, 1}},
    {{.9, -.9, 0}, {1, 0, 0, 1}},
    {{-.9, .9, 0}, {1, 0, 0, 1}},
    {{.9, .9, 0}, {1, 0, 0, 1}},
};

// These are the trianges. Just reference the vertices
const GLubyte Indices[] = {
    0, 1, 2,
    2, 1, 3
};

修改

尝试评论更新的第二部分：

/* // Set the projection matrix of the effect. It defines the field of view float aspect = fabsf(self.view.bounds.size.width / self.view.bounds.size.height); GLKMatrix4 projectionMatrix = GLKMatrix4MakePerspective(GLKMathDegreesToRadians(65.0f), aspect, 40., 10.0); self.effect.transform.projectionMatrix = projectionMatrix; // Rotate about z axis // the model view matrix is the transform applied to any geometry that the effect renders GLKMatrix4 modelViewMatrix = GLKMatrix4MakeTranslation(0, 0, -6); _rotation += 90 * self.timeSinceLastUpdate; modelViewMatrix = GLKMatrix4Rotate(modelViewMatrix, GLKMathDegreesToRadians(_rotation), 0, 0, 1); self.effect.transform.modelviewMatrix = modelViewMatrix; */

您定义的矩阵将您的对象置于最终图像之外。当您在屏幕上看不到任何内容时，您应该检查的第一件事就是转换矩阵。在您的情况下，问题在于透视转换：

GLKMatrix4 projectionMatrix = GLKMatrix4MakePerspective(GLKMathDegreesToRadians(65.0f), aspect, 40., 10.0);

您的平移和旋转对象必须位于此调用的第3个和第4个参数之间的距离才能绘制，实际上第3个参数是所谓的 near 平面的距离，并且必须小于第4个参数 far 平面。这两个参数的安全赌注通常为1和100。

GLKMatrix4 projectionMatrix = GLKMatrix4MakePerspective(GLKMathDegreesToRadians(65.0f), aspect, 1.0, 100.0);

修改2

以下是工作版本。

// // HelloGLKitViewController.m // OpenGL2Tutorial // // Created by Sean Hess on 4/10/13. // Copyright (c) 2013 Sean Hess. All rights reserved. // #import "HelloGLKitViewController.h" typedef struct { float Position[3]; float Color[4]; } Vertex; // these are not TRIANGLES, they are vertices const Vertex Vertices[] = { {{-.9, -.9, 0}, {1, 0, 0, 1}}, {{.9, -.9, 0}, {1, 0, 0, 1}}, {{-.9, .9, 0}, {1, 0, 0, 1}}, {{.9, .9, 0}, {1, 0, 0, 1}}, }; // These are the trianges. Just reference the vertices const GLubyte Indices[] = { 0, 1, 2, 2, 1, 3 }; @interface HelloGLKitViewController () { GLuint _vertexBuffer; GLuint _indexBuffer; float _rotation; float _currentRed; BOOL _increasing; } @property (nonatomic, strong) EAGLContext * context; @property (nonatomic, strong) GLKBaseEffect * effect; @end @implementation HelloGLKitViewController // I think this method just fills the objective-c stuff with the information from my c structs - (void)setupGL { [EAGLContext setCurrentContext:self.context]; self.effect = [GLKBaseEffect new]; glGenBuffers(1, &_vertexBuffer); // supposed to be an array of buffers, doing that trick again glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer); // when I say "GL_ARRAY_BUFFER" I mean _vertexBuffer glBufferData(GL_ARRAY_BUFFER, sizeof(Vertices), Vertices, GL_STATIC_DRAW); glGenBuffers(1, &_indexBuffer); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _indexBuffer); glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(Indices), Indices, GL_STATIC_DRAW); } - (void)tearDownGL { [EAGLContext setCurrentContext:self.context]; glDeleteBuffers(1, &_vertexBuffer); glDeleteBuffers(1, &_indexBuffer); self.effect = nil; } - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view. self.context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2]; if (!self.context) NSLog(@"FAiled to create ES Context"); GLKView * view = (GLKView *)self.view; view.context = self.context; // will automatically pause when interrupted self.pauseOnWillResignActive = YES; [self setupGL]; } - (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; // Dispose of any resources that can be recreated. [self tearDownGL]; } #pragma mark - GLKViewDelegate - (void)glkView:(GLKView *)view drawInRect:(CGRect)rect { glClearColor(_currentRed, 0.0, 0.0, 1.0); glClear(GL_COLOR_BUFFER_BIT); // have to call after you change any properties in the effect, before drrawing [self.effect prepareToDraw]; // We don't have to do this again, since we did it above in setupGL // They're already bound to GL_ARRAY_BUFFER and GL_ELEMENT_ARRAYBUFFER glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _indexBuffer); // remember my vertex array contains Vertex(s) // so we're telling it how to read it // position is 3 floats, the offset is based on that offsetof function glEnableVertexAttribArray(GLKVertexAttribPosition); glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid*) offsetof(Vertex, Position)); glEnableVertexAttribArray(GLKVertexAttribColor); glVertexAttribPointer(GLKVertexAttribColor, 4, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid*) offsetof(Vertex, Color)); // 1. pretty much always use triangles // 2. the number of vertices to render. tricky way to do .length on array // 3. the data type // 4. seems like should be pointer to indices. We're using VBOs, so it's already set to the GL_ELEMENT_ARRAY_BUFFER. So give it 0. glDrawElements(GL_TRIANGLES, sizeof(Indices)/sizeof(Indices[0]), GL_UNSIGNED_BYTE, 0); } - (void)update { if (_increasing) { _currentRed += 1.0 * self.timeSinceLastUpdate; } else { _currentRed -= 1.0 * self.timeSinceLastUpdate; } if (_currentRed >= 1.0) { _currentRed = 1.0; _increasing = NO; } if (_currentRed <= 0.0) { _currentRed = 0.0; _increasing = YES; } // Set the projection matrix of the effect. It defines the field of view float aspect = fabsf(self.view.bounds.size.width / self.view.bounds.size.height); GLKMatrix4 projectionMatrix = GLKMatrix4MakePerspective(GLKMathDegreesToRadians(65.0f), aspect, 1.0, 100.0); self.effect.transform.projectionMatrix = projectionMatrix; // Rotate about z axis // the model view matrix is the transform applied to any geometry that the effect renders GLKMatrix4 modelViewMatrix = GLKMatrix4MakeTranslation(0, 0, -6); _rotation += 90 * self.timeSinceLastUpdate; modelViewMatrix = GLKMatrix4Rotate(modelViewMatrix, GLKMathDegreesToRadians(_rotation), 0, 0, 1); self.effect.transform.modelviewMatrix = modelViewMatrix; } - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { self.paused = !self.paused; NSLog(@"timeSinceLastUpdate: %f", self.timeSinceLastUpdate); NSLog(@"timeSinceLastDraw: %f", self.timeSinceLastDraw); NSLog(@"timeSinceFirstResume: %f", self.timeSinceFirstResume); NSLog(@"timeSinceLastResume: %f", self.timeSinceLastResume); } @end

glDrawElements没有显示任何内容

1 个答案: