ios - OpenGL 层在 presentRenderBuffer 上变黑

Question

我有一个 child 绘图应用程序，在 iOS 6 和 7 上运行良好。现在尝试该应用程序在 iOS 8.1 上的运行方式，我只发现了一个错误。

绘图上下文已正确初始化，但是当我画一条线时，背景突然变黑(而不是默认的白色)但线是正确绘制的，使用不同的着色器(铅笔、画笔、记号笔.. .)

这是黑屏的代码

- (void)renderLineFromPoint:(CGPoint)start toPoint:(CGPoint)end 
{
static GLfloat*     vertexBuffer = NULL;
static NSUInteger   vertexMax = 64;
NSUInteger          vertexCount = 0,
count,
i;

[EAGLContext setCurrentContext:context];
glBindFramebuffer(GL_FRAMEBUFFER, viewFramebuffer);

// Convert locations from Points to Pixels
CGFloat scale = self.contentScaleFactor;
start.x *= scale;
start.y *= scale;
end.x *= scale;
end.y *= scale;

// Allocate vertex array buffer
if(vertexBuffer == NULL)
    vertexBuffer = malloc(vertexMax * 2 * sizeof(GLfloat));

// Add points to the buffer so there are drawing points every X pixels
count = MAX(ceilf(sqrtf((end.x - start.x) * (end.x - start.x) + (end.y - start.y) * (end.y - start.y)) / kBrushPixelStep), 1);
for(i = 0; i < count; ++i) {
    if(vertexCount == vertexMax) {
        vertexMax = 2 * vertexMax;
        vertexBuffer = realloc(vertexBuffer, vertexMax * 2 * sizeof(GLfloat));
    }

    vertexBuffer[2 * vertexCount + 0] = start.x + (end.x - start.x) * ((GLfloat)i / (GLfloat)count);
    vertexBuffer[2 * vertexCount + 1] = start.y + (end.y - start.y) * ((GLfloat)i / (GLfloat)count);
    vertexCount += 1;
}

// Load data to the Vertex Buffer Object
glBindBuffer(GL_ARRAY_BUFFER, vboId);
glBufferData(GL_ARRAY_BUFFER, vertexCount*2*sizeof(GLfloat), vertexBuffer, GL_DYNAMIC_DRAW);

glEnableVertexAttribArray(ATTRIB_VERTEX);
glVertexAttribPointer(ATTRIB_VERTEX, 2, GL_FLOAT, GL_FALSE, 0, 0);

// Draw
// glUseProgram(program[PROGRAM_POINT].id);
glDrawArrays(GL_POINTS, 0, vertexCount);

// Display the buffer
glBindRenderbuffer(GL_RENDERBUFFER, viewRenderbuffer);
[context presentRenderbuffer:GL_RENDERBUFFER];

self.mustSave = YES;
}

这是initGL代码

- (BOOL)initGL
{
// Generate IDs for a framebuffer object and a color renderbuffer
glGenFramebuffers(1, &viewFramebuffer);
glGenRenderbuffers(1, &viewRenderbuffer);

glBindFramebuffer(GL_FRAMEBUFFER, viewFramebuffer);
glBindRenderbuffer(GL_RENDERBUFFER, viewRenderbuffer);
// This call associates the storage for the current render buffer with the EAGLDrawable (our CAEAGLLayer)
// allowing us to draw into a buffer that will later be rendered to screen wherever the layer is (which corresponds with our view).
[context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(id<EAGLDrawable>)self.layer];
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, viewRenderbuffer);

glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &backingWidth);
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &backingHeight);

// For this sample, we do not need a depth buffer. If you do, this is how you can create one and attach it to the framebuffer:
//    glGenRenderbuffers(1, &depthRenderbuffer);
//    glBindRenderbuffer(GL_RENDERBUFFER, depthRenderbuffer);
//    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, backingWidth, backingHeight);
//    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthRenderbuffer);

if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
{
    NSLog(@"failed to make complete framebuffer object %x", glCheckFramebufferStatus(GL_FRAMEBUFFER));
    return NO;
}

// Setup the view port in Pixels
glViewport(0, 0, backingWidth, backingHeight);

// Create a Vertex Buffer Object to hold our data
glGenBuffers(1, &vboId);

// Load the brush texture
brushTexture = [self textureFromName:kStrokePatternPencil];

// Load shaders
[self setupShaders];

// Enable blending and set a blending function appropriate for premultiplied alpha pixel data
glEnable(GL_BLEND);
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);

return YES;
}

我忽略了 iOS 8 的任何问题吗？

Answer 1

鉴于您没有调用 glClear，我猜测您希望帧缓冲区的内容跨帧保留。在 iOS 上的 OpenGL ES 中，情况并非总是如此，它可能取决于 GPU 和 iOS 版本。当不保留帧缓冲区时，它会像您所描述的那样变黑。

请参阅此链接:Working with EAGLContexts 。具体来说，标题为“将结果呈现给核心动画”的部分

如果您使用 CAEAGLLayer 渲染 OpenGL ES 内容，那么您可以像这样设置保留属性:

eaglLayer.drawableProperties = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithBool:TRUE], kEAGLDrawablePropertyRetainedBacking, kEAGLColorFormatRGBA8, kEAGLDrawablePropertyColorFormat, nil];

(重要的部分是 kEAGLDrawablePropertyRetainedBacking 设置为 true)