OpenGL: 基本幾何圖形之一

since: 2012/04/27
update: 2012/04/28
reference:
OpenGL: A Primer, 3/e

基本幾何圖形之一: 點

A. 說明:
     1. 延續之前文章: I touchs: OpenGL: General Strucure 的專案.

     2. 將繪圖函式額外獨立成 .h 與 .cpp 檔案.

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B. 新增給繪圖函式使用的檔案:
     1. Xcode > File > New > File...
         > Mac OS X > C and C++ > Header File > Next

              Save As: draw.h

              Targets: OpenGLStart checked
              > Create

     2. Xcode > File > New > File...
         > Mac OS X > C and C++ > C++ File > Next

              Save As: draw.cpp

              Targets: OpenGLStart checked
              > Create

     3. 開啓 draw.h 檔案, 修改如下:
//@update
/*
#ifndef OpenGLStart_draw_h
#define OpenGLStart_draw_h

#endif
*/

     4. 開啓 draw.cpp 檔案, 修改如下:
//#include <iostream>
//@add
#include <OpenGL/OpenGL.h>
#include <GLUT/GLUT.h>

     5. 開啓 main.cpp 檔案, 修改如下:
#include <OpenGL/OpenGL.h>
#include <GLUT/GLUT.h>
#include "draw.h"
....

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C. 畫點

     1. 開啓 draw.h 檔案, 修改如下:
//@add: drawing
void drawPoints(); // 畫點

     2. 開啓 draw.cpp 檔案, 修改如下:
....
//@add: drawing
//
// 畫點
void drawPoints()
{
    // Clear the buffer
    glClear(GL_COLOR_BUFFER_BIT);
   
    //@add: Set the color for this polygon (Red)
    //
    //state: current drawing color
    //glColor3f(1.0, 0.0, 0.0);
   
    //@add: sets the point size state variable
    //
    // default: 1.0
    // p.s. glPointSize() 只能在 glBegin() 與 glEnd() 區間之外設定.  
    glPointSize(10.0);
   
    // Let us begin drawing some points
    //glBegin(GL_POLYGON);
    glBegin(GL_POINTS);
   
    // Specify the points
    glColor3f(1.0, 1.0, 1.0); // Set the color state: white
    glVertex2f(-0.5, -0.5);
   
    glColor3f(1.0, 0.0, 0.0); // Set the color state: red
    glVertex2f(-0.5, 0.5);
   
    glColor3f(0.0, 1.0, 0.0); // Set the color state: green
    glVertex2f(0.5, 0.5);
   
    glColor3f(0.0, 0.0, 1.0); // Set the color state: blue
    glVertex2f(0.5, -0.5);
   
    // Ok we are done specifying points
    glEnd();
   
    // Write this out to the screen
    glFlush();
}

     3. 開啓 main.cpp 檔案, 修改如下:
....
int main(int argc, char * argv[])
{
....
    // Set the callback function, will be called as needed
    //glutDisplayFunc(display);
    glutDisplayFunc(drawPoints); // 畫點
....
}

     4. 編譯並執行: