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Thread & Locks

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Threads Threads are subunits of processes, which can be scheduled independently by the operating system scheduler. Multiple threads can be executed at the same time on a single CPU core. The operating system assigns small slices of computing time to each thread, so that it seems to the user as if multiple tasks are executed at the same time. If multiple CPU cores are available, then multiple threads can be executed truly in parallel. We can either use the POSIX thread API, or the Objective-C wrapper around this API, NSThread. NSThread is a simple Objective-C wrapper around pthreads. Grand Central Dispatch With GCD you don’t interact with threads directly anymore. Instead you add blocks of code to queues, and GCD manages a thread pool behind the scenes. GCD decides on which particular thread your code blocks are going to be executed on, and it manages these threads according to the available system resources. This alleviates the problem of too many threads being cre
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Opengl-es Buffer

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Framebuffer A  Framebuffer  is a collection of buffers that can be used as the destination for rendering. OpenGL has two kinds of framebuffers: the  Default Framebuffer , which is provided by the  OpenGL Context ; and user-created framebuffers called  Framebuffer Objects  (FBOs). The buffers for default framebuffers are part of the context and usually represent a window or display device. The buffers for FBOs reference images from either  Textures  or  Renderbuffers ; they are never directly visible. Default Framebuffer The Default Framebuffer is the Framebuffer that OpenGL is created with. It is created along with the OpenGL Context. Like Framebuffer Objects , the default framebuffer is a series of images. Unlike FBOs, one of these images usually represents what you actually see on some part of your screen. Framebuffer Object FBO contains a collection of rendering destinations; color, depth and stencil buffer. These logical buffers in a FBO are called framebuffer-attachab
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Opengl Stages of Vertex Transformation

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Stages of Vertex Transformation Required to render the desired scene of a 3d world in a 2d screen Object Coordinates : local coordinate system of object before any transformation is applied. Eye coordinates : the result of multiplication of GL_MODELVIEW matrix and object coordinates. Objects are transformed from object space to eye space. M(ModelView) = M(view). M(model) where M(model) = object space to world space and M(view) = world space to eye space. Clip coordinates : the result of multiplication of GL_PROJECTION matrix and eye coordinates. GL_PROJECTION matrix used to define the frustum. It determined hot the 3D scene is projected onto the screen. NDC : Perspective division which is yielded by dividing the clip coordinates by w. Window coordinates : NDC are scaled and translated in order to fit into the rendering screen. Analogy With a Camera Transformations : Viewing Transformation : Setting up tripod and pointing the camera at the scene.
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