opengl大侠请进:几个红宝书相关的问题

[hkjhaha]

最近，学习opengl, 课本：opengl红宝书；
有两个问题比较疑惑：
1、按照红宝书上说：opengl坐标系的z正向指向屏幕外，实际代码测试，发现z指向屏幕里面，这是怎么回事？
2、glOrtho()函数如下设置以后，视线的方向是从（0.0, 0.0f, 0.0f)看向Z正向，还是Z负向？
3、如果下面代码，glOrtho的最后两个参数near, far的正负交换一下，这时候,视线的方向是从（0.0, 0.0f, 0.0f)看向Z正向，还是Z负向？此时会不会影响到glRotatef旋转方向（实际代码测试，好像是有影响的)？

GLfloat nRange = 100.0;

w = ClientWidth;
h = ClientHeight;

if(h == 0)
h = 1;

glViewport(0, 0, w, h);


glMatrixMode(GL_PROJECTION);
glLoadIdentity();

if (w <= h)
glOrtho (-nRange, nRange, -nRange*h/w, nRange*h/w, -nRange, nRange);
else
glOrtho (-nRange*w/h, nRange*w/h, -nRange, nRange, -nRange, nRange);


glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

[xsc2001]

你对坐标系进行旋转了吧？

[wohaoku]

只能支持了，看不懂了。

[VsirSoft]

OPENGL HOHO 算法

[jinjazz]

右手系,z指向你

[dtor]

帮顶

[yale13]

解答：
1.z正向指向屏幕外
2.此时视线指向z负向
3.交换之后指向z正向，会影响方向，因为屏幕上显示的是你看到的，你反着去看一个东西旋转，当然不一样了~
至于你的所谓测试，不知道你是怎么测试的，而且可能如2l所说，你做坐标旋转了吧？

[giant1st]

3楼的回答是正解！
请楼主注意： glMatrixMode(GL_MODELVIEW);后
MODELVIEW矩阵 是由模型 和 视点的相对变换来决定的，例如后移模型，就是前移 视点，估计你的方向弄反了与这有关！
另一个 关于变换 易犯得错误是：包括旋转，平移在内的操作是 相对于局部坐标 还是全局坐标进行的！

[sanshao27]

帮忙顶

[hkjhaha]

贴个代码，bcb的，不过很好改成vc的，好像旋转方向不对啊！

TForm1 *Form1;
HGLRC g_hrc =  NULL;
HDC g_hdc = NULL;
int g_iFontList = 0;


//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
        : TForm(Owner)
{
        Application->OnIdle = IdleLoop;
}
//---------------------------------------------------------------------------
void __fastcall TForm1::IdleLoop(TObject*, bool& done)
{
        //TODO: Add your source code here
        done = false;

        RenderScene ();

        SwapBuffers (g_hdc);
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormCreate(TObject *Sender)
{
        g_hdc = GetDC (Handle);

        SetDCPixelFormat (g_hdc);

        g_hrc = wglCreateContext (g_hdc);

        wglMakeCurrent (g_hdc, g_hrc);

        SetRC (g_hdc);
}
//---------------------------------------------------------------------------
// 设置pixel格式
void __fastcall TForm1::SetDCPixelFormat(HDC hdc)
{
        //TODO: Add your source code here
        int iPixelFormat;

        PIXELFORMATDESCRIPTOR pfd = {
                sizeof (pfd),
                1,
                PFD_DRAW_TO_WINDOW |
                PFD_SUPPORT_OPENGL |
                PFD_DOUBLEBUFFER,
                PFD_TYPE_RGBA,
                32,
                0, 0, 0, 0, 0, 0,
                0, 0,
                0, 0, 0, 0, 0,
                16,
                0,
                0,
                0,
                0,
                0,
                0,
                0};

        iPixelFormat = ChoosePixelFormat (g_hdc, &pfd);

        SetPixelFormat (g_hdc, iPixelFormat, &pfd);
}
// -----------------------------------------------------------------------
void __fastcall TForm1::SetRC(HDC hdc)
{
        //TODO: Add your source code here
        HFONT hFont;

        GLYPHMETRICSFLOAT agmf[128];

        LOGFONT logfont;

        logfont.lfHeight = -10;
        logfont.lfWidth = 0;
        logfont.lfEscapement = 0;
        logfont.lfOrientation = 0;
        logfont.lfWeight = FW_BOLD;
        logfont.lfItalic = FALSE;
        logfont.lfUnderline = FALSE;
        logfont.lfStrikeOut = FALSE;
        logfont.lfCharSet = ANSI_CHARSET;
        logfont.lfOutPrecision = OUT_DEFAULT_PRECIS;
        logfont.lfClipPrecision = CLIP_DEFAULT_PRECIS;
        logfont.lfQuality = DEFAULT_QUALITY;
        logfont.lfPitchAndFamily = DEFAULT_PITCH;
        lstrcpy (logfont.lfFaceName, "Arial");

        hFont = CreateFontIndirect (&logfont);

        SelectObject (g_hdc, hFont);


        g_iFontList = glGenLists (128);
        wglUseFontOutlines (g_hdc, 0, 128, g_iFontList, 0.0f, 0.5f,
                WGL_FONT_POLYGONS, agmf);
        DeleteObject (hFont);

        glClearColor (0.0f, 0.0f, 0.0f, 1.0f);
        glColor3f (0.0f, 1.0f, 0.0f);

        glEnable (GL_DEPTH_TEST);
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormDestroy(TObject *Sender)
{
        wglMakeCurrent (g_hdc, NULL);

        wglDeleteContext (g_hrc);

        ReleaseDC (Handle, g_hdc);

}
//---------------------------------------------------------------------------

void __fastcall TForm1::FormResize(TObject *Sender)
{
        ChangeSize (ClientWidth, ClientHeight);
}
#define ORTHO 0
void __fastcall TForm1::ChangeSize(int w, int h)
{
    GLfloat nRange = 100.0;

    w = ClientWidth;
    h = ClientHeight;

    if(h == 0)
    	h = 1;

    glViewport(0, 0, w, h);


    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

#if ORTHO
    if (w <= h)
        glOrtho (-nRange, nRange, -nRange*h/w, nRange*h/w, -nRange, nRange);
    else
	glOrtho (-nRange*w/h, nRange*w/h, -nRange, nRange, -nRange, nRange);

#else
    //For perspective correction
    GLfloat aspect = (GLfloat)w/(GLfloat)h;
    gluPerspective(60.0f, aspect, 1.0, 400.0);
#endif


    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}
//---------------------------------------------------------------------------

void __fastcall TForm1::FormPaint(TObject *Sender)
{
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        glFlush();
}
#define PI      3.1415f
GLfloat xRot = 0.0f, yRot = 0.0f;
#include "math.h"
#include "stdio.h"
//---------------------------------------------------------------------------
void __fastcall TForm1::RenderScene (void)
{

        //TODO: Add your source code here
        glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        GLfloat x, y, z, angle;

        glPushMatrix ();
#if (ORTHO == 0)
        glTranslatef (0.0f, 0.0f, -200.0f);
#endif
        glRotatef (xRot, 1.0f, 0.0f, 0.0f);
        glRotatef (yRot, 0.0f, 1.0f, 0.0f);

        glBegin (GL_LINES);
        glVertex3f (0.0f, 0.0f, -50.0f);
        glVertex3f (50.0f, 0.0f, -50.0f);
        glEnd ();

        glBegin (GL_LINE_STRIP);
        z = -50.0f;
        GLfloat adi = 0.01f;
        for (angle = 0.0f; angle <= (2.0f * PI) * 3.0f; angle += 0.1f)
        {
                x = 50.0f * sin(angle);
                y = 50.0f * cos(angle);

                glVertex3f (x, y, z);

                z += 0.5f;

        }
        glEnd ();

        glPopMatrix ();

        char cBuff[200];
        sprintf (cBuff, "xRot:%f yRot:%f", xRot, yRot);
        Caption = cBuff;
}
void __fastcall TForm1::FormKeyDown(TObject *Sender, WORD &Key,
      TShiftState Shift)
{
        if (Key == VK_UP)
        {
                xRot += 1.0f;
        }
        else if (Key == VK_DOWN)
        {
                xRot -= 1.0f;
        }
        else if (Key == VK_LEFT)
        {
                yRot += 1.0f;
        }
        else if (Key == VK_RIGHT)
        {
                yRot -= 1.0f;
        }
}