版本記錄

前言

OpenGL ES圖形庫項目中一直也沒用過，最近也想學著使用這個圖形庫，感覺還是很有意思，也就自然想著好好的總結一下，希望對大家能有所幫助。下面就開始進行實踐，寫一些小程序。感興趣的可以看上面幾篇文章。
1. OpenGL ES實踐（一）—— 一個簡單的小程序

功能需求

畫一個簡單的三角形。

功能實現

下面我們就直接看代碼。

1. JJOpenglesVC.h

#import <UIKit/UIKit.h>
#import <GLKit/GLKit.h>

@interface JJOpenglesVC : GLKViewController

@end

2. JJOpenglesVC.m

#import "JJOpenglesVC.h"

@interface JJOpenglesVC()
{
    GLuint vertexBufferID;
}

@property (strong, nonatomic) GLKBaseEffect *baseEffect;

@end

@implementation JJOpenglesVC

@synthesize baseEffect;

/////////////////////////////////////////////////////////////////
// This data type is used to store information for each vertex
//這個結構體用于存放頂點數據
typedef struct {
    GLKVector3  positionCoords;
}SceneVertex;

/////////////////////////////////////////////////////////////////
// Define vertex data for a triangle to use in example
//定義例子中三角形需要的頂點數據
static const SceneVertex vertices[] =
{
    {{-0.5f, -0.5f, 0.0}}, // lower left corner
    {{ 0.5f, -0.5f, 0.0}}, // lower right corner
    {{-0.5f,  0.5f, 0.0}}  // upper left corner
};

#pragma mark - Override Base Function

- (void)viewDidLoad
{
    // Verify the type of view created automatically by the
    // Interface Builder storyboard
    GLKView *view = (GLKView *)self.view;
    NSAssert([view isKindOfClass:[GLKView class]],
             @"View controller's view is not a GLKView");
    
    // Create an OpenGL ES 2.0 context and provide it to the
    // view
    view.context = [[EAGLContext alloc]
                    initWithAPI:kEAGLRenderingAPIOpenGLES3];
    
    // Make the new context current
    [EAGLContext setCurrentContext:view.context];
    
    // Create a base effect that provides standard OpenGL ES 3.0
    // Shading Language programs and set constants to be used for
    // all subsequent rendering
    self.baseEffect = [[GLKBaseEffect alloc] init];
    self.baseEffect.useConstantColor = GL_TRUE;
    self.baseEffect.constantColor = GLKVector4Make(
                                                   0.7f, // Red
                                                   0.6f, // Green
                                                   0.4f, // Blue
                                                   1.0f);// Alpha
    
    // Set the background color stored in the current context
    glClearColor(1.0f, 1.0f, 1.0f, 1.0f); // background color
    
    // Generate, bind, and initialize contents of a buffer to be
    // stored in GPU memory
    glGenBuffers(1,                // STEP 1
                 &vertexBufferID);
    glBindBuffer(GL_ARRAY_BUFFER,  // STEP 2
                 vertexBufferID);
    glBufferData(                  // STEP 3
                 GL_ARRAY_BUFFER,  // Initialize buffer contents
                 sizeof(vertices), // Number of bytes to copy
                 vertices,         // Address of bytes to copy
                 GL_STATIC_DRAW);  // Hint: cache in GPU memory
}

/////////////////////////////////////////////////////////////////
// Called when the view controller's view has been unloaded
// Perform clean-up that is possible when you know the view
// controller's view won't be asked to draw again soon.
- (void)viewDidUnload
{
    [super viewDidUnload];
    
    // Make the view's context current
    GLKView *view = (GLKView *)self.view;
    [EAGLContext setCurrentContext:view.context];
    
    // Delete buffers that aren't needed when view is unloaded
    if (0 != vertexBufferID)
    {
        glDeleteBuffers (1,          // STEP 7
                         &vertexBufferID);
        vertexBufferID = 0;
    }
    
    // Stop using the context created in -viewDidLoad
    ((GLKView *)self.view).context = nil;
    [EAGLContext setCurrentContext:nil];
}

#pragma mark - GLKViewDelegate

/////////////////////////////////////////////////////////////////
// GLKView delegate method: Called by the view controller's view
// whenever Cocoa Touch asks the view controller's view to
// draw itself. (In this case, render into a frame buffer that
// shares memory with a Core Animation Layer)
- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect
{
    [self.baseEffect prepareToDraw];
    
    // Clear Frame Buffer (erase previous drawing)
    glClear(GL_COLOR_BUFFER_BIT);
    
    // Enable use of positions from bound vertex buffer
    glEnableVertexAttribArray(      // STEP 4
                              GLKVertexAttribPosition);
    
    glVertexAttribPointer(          // STEP 5
                          GLKVertexAttribPosition,
                          3,                   // three components per vertex
                          GL_FLOAT,            // data is floating point
                          GL_FALSE,            // no fixed point scaling
                          sizeof(SceneVertex), // no gaps in data
                          NULL);               // NULL tells GPU to start at
    // beginning of bound buffer
    
    // Draw triangles using the first three vertices in the
    // currently bound vertex buffer
    glDrawArrays(GL_TRIANGLES,      // STEP 6
                 0,  // Start with first vertex in currently bound buffer
                 3); // Use three vertices from currently bound buffer
}

@end

功能效果

下面我們看一下功能效果。

后記

未完，待續~~~