编辑：我已经自己解决了其中的一个问题——它在模拟器上崩溃的问题。某种程度上来说，我现在可以绘制较小的模型，但是较大的模型（例如测试警车）仍会导致EXC_BAD_ACCESS，即使这是唯一的glDrawElements调用。我还能够修复在模拟器上绘制多个网格的问题。然而，我不知道这是否可以在设备上运行，直到明天早上。 (我的5.0测试设备是我朋友的iPhone，所以...）。所以我想问的主要问题是，为什么在模拟器上会因为较大的模型导致EXC_BAD_ACCESS错误？
以下是原始帖子：
然而，在升级到iOS 5.0时，我遇到了一些OpenGL ES 2.0错误——具体来说是两个错误，尽管它们可能有关联。第一个错误很简单——如果我尝试在设备上渲染我的模型（iPhone 4S运行5.0.1），它可以正常显示，但如果我尝试在模拟器上显示它（iPhone模拟器运行5.0），它会在glDrawElements上抛出EXC_BAD_ACCESS。第二个错误也很简单，我不能绘制多个网格。当我将模型作为一个大组（一个顶点数组/索引数组组合）绘制时，它可以正常绘制，但是当我将模型作为多个部分（例如，多次调用drawElements）绘制时，它会失败并显示一个黑屏——黑色不是由正在绘制的模型造成的（我已经验证了这一点，在下面进行了概述）。
总之，在模拟器上尝试渲染我的模型会导致崩溃。
注意：对于小型网格，一切都正常。我没有问题重复地绘制我的小立方体，即使在模拟器上也是如此。当我说“模型”时，我指的是一个整体模型，可能由多个顶点和索引缓冲区组成。在代码中，这意味着“模型只是保存网格或模型组数组”的一个。网格或模型组是模型的子单元，例如模型的一个连续片段，具有一个顶点数组和一个索引数组，并存储两者的长度。在我使用的模型的情况下，汽车的主体是一个网格，窗户是另一个网格，灯是第三个网格。所有这些组合在一起，构成了整个模型。
我使用的模型是一辆警车，有数千个顶点和面，分为多个部分（车身、灯光、窗户等）-车身约有3000个面，窗户约有100个，灯光略少。
以下是需要注意的几点：
My model is loading properly. I have verified this in two ways - printing out the model vertices and manually inspecting them, and displaying each model-group individually as outlined in 2). I'd post images, but 'reputation limit' and this being my first question, I can't. I have also re-built the model loader twice from scratch with no change, so I know the vertex and index buffers are in the correct order/format.
When I load the model as a single model-group (ie, one vertex buffer/index buffer) it displays the whole model correctly. When I load the model as multiple model-groups, and display any given model-group individually, it displays correctly. When I try to draw multiple model-groups (multiple calls to glDrawElements) the big black screen happens.
The black screen is not because of the model being drawn. I verified this by changing my fragment shader to draw every pixel red no matter what. I always clear the color buffer to a medium-gray (I clear the depth buffer as well, obviously), but attempting to draw multiple meshes/model-groups results in a black screen. We know it is not the model simply obscuring the view because it is colored black instead of red. This occurs on the device, I do not know what would happen on the simulator as I cannot get it to draw.
My model will not draw in the simulator. It will not draw as either a single mesh/model-group, nor multiple mesh/model-groups. The application loads properly, but attempting to draw a mesh/model-group results in an EXC_BAD_ACCESS in the glDrawElements. The relevant parts of the backtrace are:
thread #1: tid = 0x1f03, 0x10b002b5, stop reason = EXC_BAD_ACCESS (code=1, address=0x94fd020) frame #0: 0x10b002b5 frame #1: 0x09744392 GLEngine`gleDrawArraysOrElements_ExecCore + 883 frame #2: 0x09742a9b GLEngine`glDrawElements_ES2Exec + 505 frame #3: 0x00f43c3c OpenGLES`glDrawElements + 64 frame #4: 0x0001cb11 MochaARC`-[Mesh draw] + 177 at Mesh.m:81EDIT: It consistently is able to draw smaller dynamically-created models (~100 faces) but the 3000 of the whole model
I was able to get it to render a much-smaller, less-complicated, but still dynamically loaded, model consisting of 192 faces / 576 vertices. I was able to display it both as a single vertex and index buffer, as well as split up into parts and rendered as multiple smaller vertex and index buffers. Attempting to draw the single-mesh model in the simulator resulted in the EXC_BAD_ACCESS still being thrown, but only on the first frame. If I force it to continue, it displays a very screwed up model, and then every frame after that, it displayed 100% fine exactly as it ought to have.
My shaders are not in error. They compile and display correctly when I use a small, statically declared vertex buffer. However, for completeness I will post them at the bottom.
以下是我的代码：
渲染循环：
glClearColor(0.65f, 0.65f, 0.65f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
//muShader is a subclass of a shader-handler I've written that tracks the active shader
//and handles attributes/uniforms
//[muShader use] just does glUseProgram(muShader.program); then
//disables the previous shader's attributes (if needed) and then
//activates its own attributes - in this case:
//it does:
// glEnableVertexAttribArray(self.position);
// glEnableVertexAttribArray(self.uv);
//where position and uv are handles to the position and texture coordinate attributes
[self.muShader use];
GLKMatrix4 model = GLKMatrix4MakeRotation(GLKMathDegreesToRadians(_rotation), 0, 1, 0);
GLKMatrix4 world = GLKMatrix4Identity;
GLKMatrix4 mvp = GLKMatrix4Multiply(_camera.projection, _camera.view);
mvp = GLKMatrix4Multiply(mvp,world);
mvp = GLKMatrix4Multiply(mvp, model);
//muShader.modelViewProjection is a handle to the shader's model-view-projection matrix uniform
glUniformMatrix4fv(self.muShader.modelViewProjection,1,0,mvp.m);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, self.policeTextureID);
//ditto on muShader.texture
glUniform1i(self.muShader.texture, 0);
for(int i=0; i < self.policeModel.count; i++)
{
//I'll expand muShader readyForFormat after this
[self.muShader readyForFormat:ModelVertexFormat];
//I'll expand mesh draw after this
[[self.policeModel meshAtIndex:i] draw];
}
muShader相关内容
muShader绑定属性和统一变量(uniforms)
我不会贴出整个muShader类的代码，这是不必要的，只需说明它正常工作即可，否则它将永远无法显示任何内容。
//here is where we bind the attribute locations when the shader is created
-(void)bindAttributeLocations
{
_position = glGetAttribLocation(self.program, "position");
_uv = glGetAttribLocation(self.program, "uv");
}
//ditto for uniforms
-(void)bindUniformLocations
{
_modelViewProjection = glGetUniformLocation(self.program, "modelViewProjection");
_texture = glGetUniformLocation(self.program, "texture");
}
muShader准备好格式化
-(void)readyForFormat:(VertexFormat)vertexFormat
{
switch (vertexFormat)
{
//... extra vertex formats removed for brevity
case ModelVertexFormat:
//ModelVertex is a struct, with the following definition:
//typedef struct{
// GLKVector4 position;
// GLKVector4 uv;
// GLKVector4 normal;
//}ModelVertex;
glVertexAttribPointer(_position, 3, GL_FLOAT, GL_FALSE, sizeof(ModelVertex), BUFFER_OFFSET(0));
glVertexAttribPointer(_uv, 3, GL_FLOAT, GL_FALSE, sizeof(ModelVertex), BUFFER_OFFSET(16));
break;
//... extra vertex formats removed for brevity
}
}
网格相关
设置顶点/索引缓冲区
//this is how I set/create the vertex buffer for a mesh/model-group
//vertices is a c-array of ModelVertex structs
// created with malloc(count * sizeof(ModelVertex))
// and freed using free(vertices) - after setVertices is called, of course
-(void)setVertices:(ModelVertex *)vertices count:(GLushort)count
{
//frees previous data if necessary
[self freeVertices];
glGenBuffers(1, &_vertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(ModelVertex) * count, vertices, GL_STATIC_DRAW);
_vertexCount = count;
}
//this is how I set/create the index buffer for a mesh/model-group
//indices is a c-array of GLushort,
// created with malloc(count * sizeof(GLushort);
// and freed using free(vertices) - after setVertices is called, of course
-(void)setIndices:(GLushort *)indices count:(GLushort)count
{
[self freeIndices];
glGenBuffers(1, &_indexBuffer);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _indexBuffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(GLushort) * count, indices, GL_STATIC_DRAW);
_indexCount = count;
}
网格绘制
//vertexBuffer and indexBuffer are handles to a vertex/index buffer
//I have verified that they are loaded properly
glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _indexBuffer);
glDrawElements(GL_TRIANGLES, _indexCount, GL_UNSIGNED_SHORT, 0);
着色器相关
顶点着色器
attribute highp vec4 position;
attribute lowp vec3 uv;
varying lowp vec3 fragmentUV;
uniform highp mat4 modelViewProjection;
uniform lowp sampler2D texture;
void main()
{
fragmentUV = uv;
gl_Position = modelViewProjection * position;
}
片段着色器
varying lowp vec3 fragmentUV;
uniform highp mat4 modelViewProjection;
uniform lowp sampler2D texture;
void main()
{
gl_FragColor = texture2D(texture,fragmentUV.xy);
//used below instead to test the aforementioned black screen by setting
//every pixel of the model being drawn to red
//the screen stayed black, so the model wasn't covering the whole screen or anything
//gl_FragColor = vec4(1,0,0,1);
}