GLKit- and – common APIS

GLKit briefly

Before you learn about the GLKit framework, attach the GLKitAPI, apple’s official documentation

GLKit framework is designed to simplify application development based on OpenGL/OpenGL ES and accelerate the development of OpenGL/OpenGL ES applications

GLKit function

• Provide high-performance Math libraries: Provide common vector, quaternion, and matrix operations.
• Texture loading: Allows various textures to be loaded in the backgroundGLKTextureLoaderClass to load the
• Common shaders are available: the following three shaders are available
  • GLKBaseEffect
  • GLKReflectionMapEffect
  • GLKSkyboxEffect
• Provides view views and view controllers: GLKView and GLKViewController
  • GLKView: provides a drawing place, inherited from UIView
  • GLKViewController: used to manage and render the contents of a drawing view, inherited from UIViewController)

Render OpenGL ES content using GLKit view

The figure below is drawn from Apple’s official document Drawing with OpenGL ES and GLKit

There are three main steps to display images through GLKit

• GLKView creation and configuration
• Draw the graph using GLKView objects and store it in the frame cache
• Data is read from the frame cache and displayed on the screen

GLKit commonly used API

GLKit texture loading

GLKTextureInfo creates OpenGL texture information

The common attributes are listed in the table

attribute	instructions
name	The name of the texture in the OpenGL context
target	The target of the texture binding
height	The height of the loaded texture
width	Load the width of the texture
textureOrigin	Loads the origin position in the texture
alphaState	Loads the alpha component state of the texture
containsMipmaps	Boolean value, whether the loaded texture contains an MIP map

GLTextureLoader simplifies loading textures from various resource files

• Initialize the

Initialization method	instructions
– initWithSharegroup:	Initialize a new texture to load into the object
– initWithShareContext:	Initialize a new texture loading object

• Load processing from a file

Loads the processing method from a file	instructions
+ textureWithContentsOfFile:options:errer:	Loads a 2D texture image from a file and creates new textures from the data
– textureWithContentsOfFile:options:queue:completionHandler:	Asynchronously loads 2D texture images from files and creates new textures based on the data

• Load processing from the URL

Load the texture method from the URL	instructions
– textureWithContentsOfURL:options:error:	Load a 2D texture image from the URL and create a new texture from the data
– textureWithContentsOfURL:options:queue:completionHandler:	Asynchronously loads a 2D texture image from the URL and creates a new texture based on the data

• Create textures from in-memory representations

Create texture methods from in-memory representation	instructions
+ textureWithContentsOfData:options:errer:	Load a 2D texture image from memory space and create a new texture based on the data
– textureWithContentsOfData:options:queue:completionHandler:	Asynchronously loads 2D texture images from memory space and creates new textures from data

• Create textures from CGImages

Create a texture method from CGImages	instructions
– textureWithCGImage:options:error:	Load a 2D texture image from a Quartz image and create a new texture from the data
– textureWithCGImage:options:queue:completionHandler:	Asynchronously loads a 2D texture image from a Quartz image and creates a new texture based on the data

• Load multidimensional create textures from the URL

Load the multidimensional create texture method from the URL	instructions
+ cabeMapWithContentsOfURL:options:errer:	Load a vertical map texture image from a single URL and create a new texture based on the data
– cabeMapWithContentsOfURL:options:queue:completionHandler:	Asynchronously loads a cube map texture image from a single URL and creates a new texture based on the data

• Create textures by loading multidimensional data from a file

File loads multidimensional data to create texture methods	instructions
+ cubeMapWithContentsOfFile:options:errer:	Load a cube map texture object from a single file and create a new texture from the data
– cubeMapWithContentsOfFile:options:queue:completionHandler:	Asynchronously loads a cube map texture object from a single file and creates a new texture from the data
+ cubeMapWithContentsOfFiles:options:errer:	Load cube map texture images from a series of files and create new textures from the data
-cubeMapWithContentsOfFiles:options:options:queue:completionHandler:	Asynchronously loads cube map texture images from a series of files and creates new textures from the data

GLKit OpenGL ES View rendering API

GLKView uses OpenGL ES as the default view for drawing content. The common API and properties are shown below

• Initialize the view

attribute	instructions
– initWithFrame:context:	Initialize the new view

• Set the agent

attribute	instructions
delegate	View proxy

• Configure the frame cache object

attribute	instructions
Configure the frame cache object	drawableColorFormat
drawableDepthFormat	Deep render cache format
drawableStencilFormat	Template render cache format
drawableMultisample	Multisample cache format

– Frame cache property

attribute	instructions
drawableHeight	Height, in pixels, of the underlying cache object
drawableWidth	The width in pixels of the underlying cache object

• Draws the contents of the view

attribute	instructions
context	Use the OpenGL ES context used to draw the view content
drawableStencilFormat	Bind the underlying FrameBuffer object to OpenGL ES
enableSetNeedsDisplay	Boolean value that specifies whether the view responds to messages that invalidate the view’s contents
snapshot	Draws the view content and returns it as a new image object

methods	instructions
– bindDrawable	Deep render cache format
– display	Redraw the view content immediately

• Delete the view FrameBuffer object

methods	instructions
– deleteDrawable	Deletes a drawable object associated with a view

GLKViewDelegate is used for the GLKView object callback method

• Draw the contents of the view (proxy must be implemented ！！！！)

attribute	instructions
– glkView:drawInRect:	Draw view content (proxy must be implemented)

GLKViewController Is a view controller that manages the OpenGL ES rendering loop

• update

methods	instructions
– (void) update	Update view content
– (void) glkViewControllerUpdate:	Update the view controller display

• Configure frame Rate

attribute	instructions
preferredFramesPerSecond	The rate at which the view controller invokes the view and updates the view content
framesPerSencond	The actual rate at which the view controller invokes the view and updates its contents

• Configure the GLKViewDelegate proxy

attribute	instructions
delegate	Proxy for the view controller

• Control frame update

ResumeOnDidBecomeActive Boolean that indicates whether the view control automatically resumes the rendering loop when the current application becomes active

attribute	instructions
paused	Boolean value, whether the render loop has been paused
pausedOnWillResignActive	Boolean value, whether the view controller automatically pauses the rendering loop when the current program reactivates the active state
resumeOnDidBecomeActive	Boolean value, which controls whether the view automatically resumes the rendering loop when the current application becomes active

• Get updated information about the View

attribute	instructions
frameDisplayed	The number of frame updates sent by the view controller since its creation
timeSinceFirstResume	The amount of time that has elapsed since the view controller first resumed sending the update event
timeSinceLastResume	The amount of time since the last time the view controller resumed sending the update event
timeSinceLastUpdate	The amount of time that has elapsed since the last view controller called the delegate method
timeSinceLastDraw	The amount of time that has elapsed since the last view controller called the delegate method

GLKViewControllerDelegate * * * * render loop callback square method

• Handles more updated events

The callback method	instructions
– glkViewControllerUpdate:	Called before displaying each frame, similar to the RenderScene function in OpenGL

• Pause/resume notification

The callback method	instructions
– glkViewController : willPause:	Called before the render loop pauses or resumes

GLKBaseEffect

A simple lighting/shading system for shader based OpenGL rendering

• Named Effect

attribute	instructions
label	Give an Effect a name

• Configure the model view transformation

attribute	instructions
transform	Binding effects are applied to vertex data model views, projections, and texture transformations

• Configure lighting effects

attribute	instructions
lightingType	Used to calculate the lighting strategy for each fragment,GLKLightingType

GLKLightingType enumeration	instructions
GLKLightingTypePerVertex	Represents performing lighting calculations on each vertex in the triangle and then interpolating in the triangle
GLKLightingTypePerPixel	The input representing the lighting calculation is inserted into the triangle, and the lighting calculation is performed on each fragment

• Configure the illumination

attribute	instructions
lightModelTwoSided	Boolean value representing computed illumination on both sides of the primitive
material	Calculates the material properties to use for rendering pixel lighting
lightModelAmbientColor	Environment color, apply the effect to render all primitives.
light0	The first lighting property in the scene
light1	The second lighting property in the scene
light2	The third lighting property in the scene

• Configure the texture

attribute	instructions
texture2d0	The first texture property
texture2d1	Second texture property
textureOrder	The order in which textures are applied to render primitives

• Configuration atomization

attribute	instructions
fog	Fog property applied to the scene

• Configuring color Information

attribute	instructions
colorMaterialEnable	A Boolean value that indicates whether the color vertex property is used when calculating light interaction with the material
useConstantColor	Boolean value indicating whether constant colors are used
constantColor	Constant color is used when no per-vertex color data is supplied

• Prepare the rendering effect

methods	instructions
– prepareToDraw	Prepare the rendering effect

Note 1: GLKit has a maximum of 3 lights and 2 textures. 2. Constant color: black