Ray-Triangle交叉點採摘不起作用

Question

過去幾天我一直在爲此工作，並一直卡住。我需要能夠觸摸屏幕並返回我的模型上最接近與拾取點處生成的光線相交的近平面的點的x，y，z座標。我認爲我的問題的一部分是我爲我的模型在整個渲染代碼中進行了一系列矩陣變換和旋轉，儘管我感興趣的幾何都是在特定的變換狀態下呈現的。我使用的代碼如下。如果任何人都可以幫助我弄清楚如何使這個工作，那將是非常棒的。 checkCollision（）提供了用戶點擊的點，gluUnProject（）應該將我的2D拾取點轉換爲我的近平面和遠平面上的三維座標，其中0爲近平面，1爲遠平面。我使用的是在這裏，被稱爲幾何形狀呈現的右前，讓所有變換已經被應用：

[self checkCollision:touchPoint panVector:panVec]; 

下面這段代碼是碰撞檢查代碼：

-(Boolean) checkCollision:(CGPoint)winPos panVector:(Vector3f*)panVec 
{ 
glGetIntegerv(GL_VIEWPORT, viewport); 

winPos.y = (float)viewport[3] - winPos.y; 

Vector3f nearPoint; 
Vector3f farPoint; 

glGetFloatv(GL_PROJECTION_MATRIX, projection); 
glGetFloatv(GL_MODELVIEW_MATRIX, modelview); 

//Retreiving position projected on near plane 
gluUnProject(winPos.x, winPos.y , 0, modelview, projection, viewport, &nearPoint.x, &nearPoint.y, &nearPoint.z); 

//Retreiving position projected on far plane 
gluUnProject(winPos.x, winPos.y, 1, modelview, projection, viewport, &farPoint.x, &farPoint.y, &farPoint.z); 

Vector3f *near = [[Vector3f alloc] initWithFloatsX:nearPoint.x Y:nearPoint.y Z:nearPoint.z]; 
Vector3f *far = [[Vector3f alloc] initWithFloatsX:farPoint.x Y:farPoint.y Z:farPoint.z]; 
Vector3f *d = [Vector3f subtractV1:far minusV2:near]; 

Vector3f *v0 = [[Vector3f alloc] init]; 
Vector3f *v1 = [[Vector3f alloc] init]; 
Vector3f *v2 = [[Vector3f alloc] init]; 
Vector3f *e1; // = [[Vector3f alloc] init]; 
Vector3f *e2; // = [[Vector3f alloc] init]; 

for (int i = 0; i < assemblyObj->numObjects; i++) { 
    for (int j = 0; j < assemblyObj->partList[i].numVertices; j+=18) { 
     v0.x = assemblyObj->partList[i].vertices[j+0]; 
     v0.y = assemblyObj->partList[i].vertices[j+1]; 
     v0.z = assemblyObj->partList[i].vertices[j+2]; 

     v1.x = assemblyObj->partList[i].vertices[j+6]; 
     v1.y = assemblyObj->partList[i].vertices[j+7]; 
     v1.z = assemblyObj->partList[i].vertices[j+8]; 

     v2.x = assemblyObj->partList[i].vertices[j+12]; 
     v2.y = assemblyObj->partList[i].vertices[j+13]; 
     v2.z = assemblyObj->partList[i].vertices[j+14]; 

     e1 = [Vector3f subtractV1:v1 minusV2:v0]; 
     e2 = [Vector3f subtractV1:v2 minusV2:v0]; 

     Vector3f *p = [[Vector3f alloc] init]; 
     [Vector3f cross:p V1:d V2:e2]; 
     float a = [Vector3f dot:e1 V2:p]; 
     if (a > -.000001 && a < .000001) { 
      continue; 
     } 

     float f = 1/a; 
     Vector3f *s = [Vector3f subtractV1:near minusV2:v0]; 
     float u = f*([Vector3f dot:s V2:p]); 
     if (u<0 || u>1) { 
      continue; 
     } 
     Vector3f *q = [[Vector3f alloc] init]; 
     [Vector3f cross:q V1:s V2:e1]; 
     float v = f*([Vector3f dot:d V2:q]); 
     if (v<0 || (u+v)>1) { 
      continue; 
     } 
     //NSLog(@"hit polygon"); 
     return true; 
    } 
} 

//NSLog(@"didn't hit polygon"); 
return FALSE; 
} 


GLint gluUnProject(GLfloat winx, GLfloat winy, GLfloat winz, 
     const GLfloat model[16], const GLfloat proj[16], 
     const GLint viewport[4], 
     GLfloat * objx, GLfloat * objy, GLfloat * objz) 
{ 
/* matrice de transformation */ 
GLfloat m[16], A[16]; 
GLfloat in[4], out[4]; 

/* transformation coordonnees normalisees entre -1 et 1 */ 
in[0] = (winx - viewport[0]) * 2/viewport[2] - 1.f; 
in[1] = (winy - viewport[1]) * 2/viewport[3] - 1.f; 
in[2] = 2 * winz - 1.f; 
in[3] = 1.f; 

/* calcul transformation inverse */ 
matmul(A, proj, model); 
invert_matrix(A, m); 

/* d'ou les coordonnees objets */ 
transform_point(out, m, in); 
if (out[3] == 0.f) 
    return GL_FALSE; 
*objx = out[0]/out[3]; 
*objy = out[1]/out[3]; 
*objz = out[2]/out[3]; 
return GL_TRUE; 
} 


void transform_point(GLfloat out[4], const GLfloat m[16], const GLfloat in[4]) 
{ 
#define M(row,col) m[col*4+row] 
out[0] = 
M(0, 0) * in[0] + M(0, 1) * in[1] + M(0, 2) * in[2] + M(0, 3) * in[3]; 
out[1] = 
M(1, 0) * in[0] + M(1, 1) * in[1] + M(1, 2) * in[2] + M(1, 3) * in[3]; 
out[2] = 
M(2, 0) * in[0] + M(2, 1) * in[1] + M(2, 2) * in[2] + M(2, 3) * in[3]; 
out[3] = 
M(3, 0) * in[0] + M(3, 1) * in[1] + M(3, 2) * in[2] + M(3, 3) * in[3]; 
#undef M 
} 

void matmul(GLfloat * product, const GLfloat * a, const GLfloat * b) 
{ 
/* This matmul was contributed by Thomas Malik */ 
GLfloat temp[16]; 
GLint i; 

#define A(row,col) a[(col<<2)+row] 
#define B(row,col) b[(col<<2)+row] 
#define T(row,col) temp[(col<<2)+row] 

/* i-te Zeile */ 
for (i = 0; i < 4; i++) { 
    T(i, 0) = 
    A(i, 0) * B(0, 0) + A(i, 1) * B(1, 0) + A(i, 2) * B(2, 0) + A(i, 
                    3) * 
    B(3, 0); 
    T(i, 1) = 
    A(i, 0) * B(0, 1) + A(i, 1) * B(1, 1) + A(i, 2) * B(2, 1) + A(i, 
                    3) * 
    B(3, 1); 
    T(i, 2) = 
    A(i, 0) * B(0, 2) + A(i, 1) * B(1, 2) + A(i, 2) * B(2, 2) + A(i, 
                    3) * 
    B(3, 2); 
    T(i, 3) = 
    A(i, 0) * B(0, 3) + A(i, 1) * B(1, 3) + A(i, 2) * B(2, 3) + A(i, 
                    3) * 
    B(3, 3); 
} 

#undef A 
#undef B 
#undef T 
memcpy(product, temp, 16 * sizeof(GLfloat)); 
} 

int invert_matrix(const GLfloat * m, GLfloat * out) 
{ 
/* NB. OpenGL Matrices are COLUMN major. */ 
#define SWAP_ROWS(a, b) { GLfloat *_tmp = a; (a)=(b); (b)=_tmp; } 
#define MAT(m,r,c) (m)[(c)*4+(r)] 

GLfloat wtmp[4][8]; 
GLfloat m0, m1, m2, m3, s; 
GLfloat *r0, *r1, *r2, *r3; 

r0 = wtmp[0], r1 = wtmp[1], r2 = wtmp[2], r3 = wtmp[3]; 

r0[0] = MAT(m, 0, 0), r0[1] = MAT(m, 0, 1), 
r0[2] = MAT(m, 0, 2), r0[3] = MAT(m, 0, 3), 
r0[4] = 1.f, r0[5] = r0[6] = r0[7] = 0.f, 
r1[0] = MAT(m, 1, 0), r1[1] = MAT(m, 1, 1), 
r1[2] = MAT(m, 1, 2), r1[3] = MAT(m, 1, 3), 
r1[5] = 1.f, r1[4] = r1[6] = r1[7] = 0.f, 
r2[0] = MAT(m, 2, 0), r2[1] = MAT(m, 2, 1), 
r2[2] = MAT(m, 2, 2), r2[3] = MAT(m, 2, 3), 
r2[6] = 1.f, r2[4] = r2[5] = r2[7] = 0.f, 
r3[0] = MAT(m, 3, 0), r3[1] = MAT(m, 3, 1), 
r3[2] = MAT(m, 3, 2), r3[3] = MAT(m, 3, 3), 
r3[7] = 1.f, r3[4] = r3[5] = r3[6] = 0.f; 

/* choose pivot - or die */ 
if (fabsf(r3[0]) > fabsf(r2[0])) 
    SWAP_ROWS(r3, r2); 
if (fabsf(r2[0]) > fabsf(r1[0])) 
    SWAP_ROWS(r2, r1); 
if (fabsf(r1[0]) > fabsf(r0[0])) 
    SWAP_ROWS(r1, r0); 
if (0.f == r0[0]) 
    return GL_FALSE; 

/* eliminate first variable  */ 
m1 = r1[0]/r0[0]; 
m2 = r2[0]/r0[0]; 
m3 = r3[0]/r0[0]; 
s = r0[1]; 
r1[1] -= m1 * s; 
r2[1] -= m2 * s; 
r3[1] -= m3 * s; 
s = r0[2]; 
r1[2] -= m1 * s; 
r2[2] -= m2 * s; 
r3[2] -= m3 * s; 
s = r0[3]; 
r1[3] -= m1 * s; 
r2[3] -= m2 * s; 
r3[3] -= m3 * s; 
s = r0[4]; 
if (s != 0.f) { 
    r1[4] -= m1 * s; 
    r2[4] -= m2 * s; 
    r3[4] -= m3 * s; 
} 
s = r0[5]; 
if (s != 0.f) { 
    r1[5] -= m1 * s; 
    r2[5] -= m2 * s; 
    r3[5] -= m3 * s; 
} 
s = r0[6]; 
if (s != 0.f) { 
    r1[6] -= m1 * s; 
    r2[6] -= m2 * s; 
    r3[6] -= m3 * s; 
} 
s = r0[7]; 
if (s != 0.f) { 
    r1[7] -= m1 * s; 
    r2[7] -= m2 * s; 
    r3[7] -= m3 * s; 
} 

/* choose pivot - or die */ 
if (fabsf(r3[1]) > fabsf(r2[1])) 
    SWAP_ROWS(r3, r2); 
if (fabsf(r2[1]) > fabsf(r1[1])) 
    SWAP_ROWS(r2, r1); 
if (0.f == r1[1]) 
    return GL_FALSE; 

/* eliminate second variable */ 
m2 = r2[1]/r1[1]; 
m3 = r3[1]/r1[1]; 
r2[2] -= m2 * r1[2]; 
r3[2] -= m3 * r1[2]; 
r2[3] -= m2 * r1[3]; 
r3[3] -= m3 * r1[3]; 
s = r1[4]; 
if (0.f != s) { 
    r2[4] -= m2 * s; 
    r3[4] -= m3 * s; 
} 
s = r1[5]; 
if (0.f != s) { 
    r2[5] -= m2 * s; 
    r3[5] -= m3 * s; 
} 
s = r1[6]; 
if (0.f != s) { 
    r2[6] -= m2 * s; 
    r3[6] -= m3 * s; 
} 
s = r1[7]; 
if (0.f != s) { 
    r2[7] -= m2 * s; 
    r3[7] -= m3 * s; 
} 

/* choose pivot - or die */ 
if (fabs(r3[2]) > fabs(r2[2])) 
    SWAP_ROWS(r3, r2); 
if (0.f == r2[2]) 
    return GL_FALSE; 

/* eliminate third variable */ 
m3 = r3[2]/r2[2]; 
r3[3] -= m3 * r2[3], r3[4] -= m3 * r2[4], 
r3[5] -= m3 * r2[5], r3[6] -= m3 * r2[6], r3[7] -= m3 * r2[7]; 

/* last check */ 
if (0.f == r3[3]) 
    return GL_FALSE; 

s = 1.f/r3[3];  /* now back substitute row 3 */ 
r3[4] *= s; 
r3[5] *= s; 
r3[6] *= s; 
r3[7] *= s; 

m2 = r2[3];   /* now back substitute row 2 */ 
s = 1.f/r2[2]; 
r2[4] = s * (r2[4] - r3[4] * m2), r2[5] = s * (r2[5] - r3[5] * m2), 
r2[6] = s * (r2[6] - r3[6] * m2), r2[7] = s * (r2[7] - r3[7] * m2); 
m1 = r1[3]; 
r1[4] -= r3[4] * m1, r1[5] -= r3[5] * m1, 
r1[6] -= r3[6] * m1, r1[7] -= r3[7] * m1; 
m0 = r0[3]; 
r0[4] -= r3[4] * m0, r0[5] -= r3[5] * m0, 
r0[6] -= r3[6] * m0, r0[7] -= r3[7] * m0; 

m1 = r1[2];   /* now back substitute row 1 */ 
s = 1.f/r1[1]; 
r1[4] = s * (r1[4] - r2[4] * m1), r1[5] = s * (r1[5] - r2[5] * m1), 
r1[6] = s * (r1[6] - r2[6] * m1), r1[7] = s * (r1[7] - r2[7] * m1); 
m0 = r0[2]; 
r0[4] -= r2[4] * m0, r0[5] -= r2[5] * m0, 
r0[6] -= r2[6] * m0, r0[7] -= r2[7] * m0; 

m0 = r0[1];   /* now back substitute row 0 */ 
s = 1.f/r0[0]; 
r0[4] = s * (r0[4] - r1[4] * m0), r0[5] = s * (r0[5] - r1[5] * m0), 
r0[6] = s * (r0[6] - r1[6] * m0), r0[7] = s * (r0[7] - r1[7] * m0); 

MAT(out, 0, 0) = r0[4]; 
MAT(out, 0, 1) = r0[5], MAT(out, 0, 2) = r0[6]; 
MAT(out, 0, 3) = r0[7], MAT(out, 1, 0) = r1[4]; 
MAT(out, 1, 1) = r1[5], MAT(out, 1, 2) = r1[6]; 
MAT(out, 1, 3) = r1[7], MAT(out, 2, 0) = r2[4]; 
MAT(out, 2, 1) = r2[5], MAT(out, 2, 2) = r2[6]; 
MAT(out, 2, 3) = r2[7], MAT(out, 3, 0) = r3[4]; 
MAT(out, 3, 1) = r3[5], MAT(out, 3, 2) = r3[6]; 
MAT(out, 3, 3) = r3[7]; 

return GL_TRUE; 

#undef MAT 
#undef SWAP_ROWS 
} 

編輯：

我跟着Justin Meiners提出渲染點的建議，告訴我在哪裏拾取光線正在生成，我可以看到現在發生了什麼，但不知道爲什麼。我的場景通過四元數實現弧球旋轉，縮放和平移。我會粗略地展示我的場景在做什麼，然後我的選擇線發生了什麼。

首先，設置我的視口：

glViewport(0, 0, scene.width, scene.height); 
glOrthof(-11.25, 11.25, -14.355, 14.355, -1000, 1000); 

接下來，我搶，我用我的軌跡球方法的一部分來瀏覽我的場景，並通過它加倍重視自己的模型視圖矩陣的16個元素矩陣：

float mat[16]; 
[arcball get_Renamed:mat]; 
glMultMatrixf(mat); 

現在，我做我的挑線：

glGetIntegerv(GL_VIEWPORT, viewport); 
glGetFloatv(GL_PROJECTION_MATRIX, projection); 
glGetFloatv(GL_MODELVIEW_MATRIX, modelview); 

touchPoint.y = (float)viewport[3] - touchPoint.y; 

Vector3f nearPoint, farPoint; 

//Retreiving position projected on near plane 
gluUnProject(touchPoint.x, touchPoint.y , 0, modelview, projection, viewport, &nearPoint.x, &nearPoint.y, &nearPoint.z); 

//Retreiving position projected on far plane 
gluUnProject(touchPoint.x, touchPoint.y, 1, modelview, projection, viewport, &farPoint.x, &farPoint.y, &farPoint.z); 

float coords[3] = {nearPoint.x, nearPoint.y, nearPoint.z}; 
float coords2[3] = {farPoint.x, farPoint.y, farPoint.z}; 

glPointSize(100); 
glColor4f(1, 0, 0, 1); 
glEnableClientState(GL_VERTEX_ARRAY); 
glVertexPointer(3, GL_FLOAT, sizeof(coords[0])*3, coords); 
glDrawArrays(GL_POINTS, 0, 1); 

glPointSize(150); 
glColor4f(0, 0, 1, 1); 
glEnableClientState(GL_VERTEX_ARRAY); 
glVertexPointer(3, GL_FLOAT, sizeof(coords2[0])*3, coords2); 
glDrawArrays(GL_POINTS, 0, 1); 
glDisableClientState(GL_VERTEX_ARRAY); 

我做這個，之前我轉動我的場景，它工作正常，但只要我開始旋轉我的場景，遠點就開始移動。如果我圍繞180度旋轉場景，則遠點將回到近點。任何想法是怎麼回事？弧球只是基於Ken Shoemake的算法。

Answer 1

我終於想通了，我在做什麼錯的。你必須得到在創建後右GL_VIEWPORT和GL_PROJECTION_MATRIX的狀態，而其

glMatrixMode(GL_PROJECTION); 
glLoadIdentity(); 

電話後馬上是，如果你這樣做以後，那麼你的矩陣轉換影響您的視d投影矩陣。看起來他們不應該這樣做，但他們確實如此。當你選擇的時候，你想要得到狀態的唯一矩陣就是模型視圖矩陣，並且當你的模型視圖與你試圖執行gluUnProject的幾何圖形具有相同的變換時，你想要這樣做。一旦我明白了這一點，射線拾取算法效果很好。在iPad上，它可以在19ms內對15,000個三角形進行三角形交線，相當於每秒約800,000個交點。對於iPad來說不算太壞，但我相信通過預先計算三角平面方程可以提高性能。感謝這些建議，他們幫助我弄清楚發生了什麼，以便我能夠修復它。

Answer 2

你應該畫出GL_LINES的鼠標光線，以確保它看起來正確。這將拯救你的生命，你可以咀嚼matricies和東西來嘗試做對。此外，如果你做了很多轉換，那麼你需要在那裏調用glUnProject，以便考慮到這些。您可能必須保存鼠標位置，直到您可以在下一個渲染循環中取消投影爲止。 EG

glPushMatrix(); 

// Rotate world 
glRotate(...) 

// Mouse glGetIntv, and glGetFloatV here 

drawObject() 

樣品圖碼（給該Vector僅僅是一個浮動的x，y和z分量結構。

glEnableClientState(GL_VERTEX_ARRAY); 
    glVertexPointer(3, GL_FLOAT, sizeof(Vector), points); 

    glDrawArrays(GL_POINTS, 0, 2); 

    glDisableClientState(GL_VERTEX_ARRAY);