过去几天我一直在努力解决这个问题。我需要能够触摸屏幕并返回我的模型上最接近与拾取点处生成的光线相交的近平面的点的x，y，z坐标。我认为我的问题的一部分是我在我的模型的渲染代码中进行了一系列矩阵变换和旋转，尽管我感兴趣的几何体都是在特定的变换状态下渲染的。我正在使用的代码如下。如果有人能帮助我弄清楚如何使这个工作，那将是非常棒的。 checkCollision（）被输入用户点击的点，而gluUnProject（）应该将我的2d拾取点转换为我的近和远平面上的3D坐标，0是近平面，1是远平面。我的用法就在这里，并在渲染几何体之前调用，因此所有变换都已应用：
[self checkCollision:touchPoint panVector:panVec];
以下代码是碰撞检查代码：
-(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
}
我跟随Justin Meiners建议渲染点向我展示我的拾取光线生成的位置，我可以看到现在发生了什么，但不知道为什么。我的场景通过四元数实现了弧形旋转，缩放和平移。我将粗略地列出我的场景正在做什么，然后我的拾取光线发生了什么。
首先，设置我的视口：
glViewport(0, 0, scene.width, scene.height);
glOrthof(-11.25, 11.25, -14.355, 14.355, -1000, 1000);
接下来，我抓住我用作我的arcball方法一部分的16个元素矩阵来导航我的场景并乘以我的模型视图矩阵：
float mat[16];
[arcball get_Renamed:mat];
glMultMatrixf(mat);
现在，我选择射线：
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);
我这样做，在旋转场景之前它工作正常，但是一旦我开始旋转我的场景，远点开始移动。如果我将场景旋转180度，则远点会与近点一致。知道发生了什么事吗？弧球基于Ken Shoemake的算法。
答案 0 :(得分：3)
您应该使用GL_LINES绘制鼠标光线，以确保它看起来正确。这将拯救你的生命，你可以调整matricies和东西来尝试正确。此外，如果您进行了大量的转换，那么您需要在其中调用glUnProject，以便考虑到这些。您可能必须保存鼠标位置，直到您可以在下一个渲染循环中取消投影。 EG
glPushMatrix();
// Rotate world
glRotate(...)
// Mouse glGetIntv, and glGetFloatV here
drawObject()
示例绘图代码（Give that Vector只是一个包含float x，y和z组件的结构。
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3, GL_FLOAT, sizeof(Vector), points);
glDrawArrays(GL_POINTS, 0, 2);
glDisableClientState(GL_VERTEX_ARRAY);
答案 1 :(得分：1)
我终于弄清楚我做错了什么。您必须在创建GL_VIEWPORT和GL_PROJECTION_MATRIX之后立即获取GL_VIEWPORT和GL_PROJECTION_MATRIX的状态，这就在
之后glMatrixMode(GL_PROJECTION);
glLoadIdentity();
呼叫。如果稍后执行此操作，则矩阵变换会影响视口和投影矩阵。它似乎不应该，但他们确实如此。您希望获得拾取时唯一的矩阵是模型视图矩阵，当模型视图与您尝试执行gluUnProject的几何体具有相同的变换时，您希望这样做。一旦我弄清楚了，光线拾取算法运作良好。在iPad上，它可以在19毫秒内对15,000个三角形执行三角形交叉，相当于每秒约800,000个交叉点。虽然我确信通过预先计算三角平面方程式可以提高性能，但对iPad来说并不算太糟糕。感谢您的建议，他们帮助我弄清楚发生了什么，所以我可以解决它。