OpenGL ES 入門: 二. 簡單繪圖之四

since: 2012/04/03
update: 2012/04/03
reference:
1. 原文:
iPhone Development: OpenGL ES From the Ground Up, Part 2: A Look at Simple Drawing

2. 翻譯:
從零開始學習OpenGL ES之二 – 簡單繪圖概述

簡單繪圖之四: 設定頂點顏色

A. 說明
      1. OpenGL ES 允許你將每個頂點使用的顏色置於一個顏色陣列 (color array) 中.

      2. 如果你選擇使用顏色陣列，那麼你需要為每個頂點設定顏色(四個 GLfloat 值).

      3. 可以通過以下的方法來啟動顏色陣列: glEnableClientState(GL_COLOR_ARRAY);

-----------------------------------------------------------------------------------

B. 開啓 OpenGLESCommon.h 檔案, 修改如下:
....
#pragma mark -
#pragma mark Color3D
#pragma mark -

// 顏色定義
typedef struct {
    GLfloat    red;
    GLfloat    green;
    GLfloat    blue;
    GLfloat    alpha;
} Color3D;

// 單個顏色
static inline Color3D Color3DMake(CGFloat inRed, CGFloat inGreen, CGFloat inBlue, CGFloat inAlpha)
{
    Color3D ret;
   
    ret.red = inRed;
    ret.green = inGreen;
    ret.blue = inBlue;
    ret.alpha = inAlpha;
   
    return ret;
}

// 設定現存顏色的值
static inline void Color3DSet(Color3D *color, CGFloat inRed, CGFloat inGreen, CGFloat inBlue, CGFloat inAlpha)
{
    color->red = inRed;
    color->green = inGreen;
    color->blue = inBlue;
    color->alpha = inAlpha;
}
....

-----------------------------------------------------------------------------------

C. 頂點顏色前置作業
      1. 開啓 GLView.h 檔案, 修改如下:
....
//@add for protocol
@protocol GLViewDelegate

@required
- (void)setupView:(GLView *)view;

@optional
//@update for drawing
- (void)drawView:(GLView *)view;
- (void)drawTriangle3D; // 畫三角形
- (void)drawSquare; // 畫正方形
- (void)drawVertexColor; // 畫頂點顏色

@end
....

      2. 開啓 ViewController.m 檔案, 修改如下:
....
// 畫頂點顏色
- (void)drawVertexColor
{
    NSLog(@"ViewController => drawVertexColor");
    // Draw code here
}
....

      3. 開啓 GLView.m 檔案, 修改如下:
....
- (void)drawView
{
....
    //@update for drawing
    //[self.delegate drawTriangle3D]; // 畫三角形
    //[self.delegate drawSquare]; // 畫正方形
    [self.delegate drawVertexColor]; // 畫頂點顏色
....
}
....

-----------------------------------------------------------------------------------

D. 開啓 ViewController.m 檔案, 修改如下:
....
// 畫頂點顏色
- (void)drawVertexColor
{
    NSLog(@"ViewController => drawVertexColor");
    // Draw code here
    Vertex3D    vertex1 = Vertex3DMake(0.0, 1.0, -3.0);
    Vertex3D    vertex2 = Vertex3DMake(1.0, 0.0, -3.0);
    Vertex3D    vertex3 = Vertex3DMake(-1.0, 0.0, -3.0);
    Triangle3D  triangle = Triangle3DMake(vertex1, vertex2, vertex3);
   
    Color3D *colors = malloc(sizeof(Color3D) * 3);
    Color3DSet(&colors[0], 1.0, 0.0, 0.0, 1.0);
    Color3DSet(&colors[1], 0.0, 1.0, 0.0, 1.0);
    Color3DSet(&colors[2], 0.0, 0.0, 1.0, 1.0);
   
    glLoadIdentity();
    glClearColor(0.7, 0.7, 0.7, 1.0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_COLOR_ARRAY);
    glColor4f(1.0, 0.0, 0.0, 1.0);
    glVertexPointer(3, GL_FLOAT, 0, &triangle);
    glColorPointer(4, GL_FLOAT, 0, colors);
    glDrawArrays(GL_TRIANGLES, 0, 9);
    glDisableClientState(GL_VERTEX_ARRAY);
    glDisableClientState(GL_COLOR_ARRAY);
   
    if (colors != NULL)
        free(colors);
}
....

-----------------------------------------------------------------------------------

E. 編譯並執行