iphone - 射线-三角形交叉点拾取不起作用

标签 iphone objective-c math opengl-es

过去几天我一直在研究这个问题，但一直被困住。我需要能够触摸屏幕并返回模型上最接近与拾取点生成的射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模型的整个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让它发挥作用，那就太棒了。 checkCollision() 被提供给用户点击的点，而 gluUnProject() 应该将我的 2d 拾取点转换为我的近平面和远平面上的 3D 坐标，0 是近平面，1 是远平面。我的用法在这里，在渲染几何图形之前调用，因此所有变换都已应用:

[self checkCollision:touchPoint panVector:panVec];

下面的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
}

编辑:

我遵循 Justin Meiners 的渲染点建议，向我展示了我的拾取光线在哪里生成，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轨迹球旋转、缩放和平移。我将粗略地列出我的场景正在做什么，然后我的选择射线正在发生什么。

首先，设置我的视口(viewport):

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

接下来，我获取 16 个元素矩阵，将其用作 arcball 方法的一部分来导航场景并将其乘以模型 View 矩阵:

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

现在，我开始挑选光线:

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);

我这样做了，在旋转场景之前它工作得很好，但是一旦我开始旋转场景，远点就开始移动。如果我将场景精确旋转 180 度，远点将与近点重新对齐。知道发生了什么事吗？轨迹球只是基于 Ken Shoemake 的算法。

最佳答案

您应该使用 GL_LINES 绘制鼠标射线以确保它看起来正确。这将挽救你的生命，你可以调整矩阵和其他东西来尝试使其正确。另外，如果您进行了大量转换，那么您需要在其中调用 glUnProject ，以便它考虑到这些。您可能必须保存鼠标位置，直到可以在下一个渲染循环中取消投影它。 EG

glPushMatrix();

// Rotate world
glRotate(...)

// Mouse glGetIntv, and glGetFloatV here

drawObject()

示例绘图代码(假设 Vector 只是一个具有 float x、y 和 z 分量的结构。

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

    glDrawArrays(GL_POINTS, 0, 2);

    glDisableClientState(GL_VERTEX_ARRAY);

关于iphone - 射线-三角形交叉点拾取不起作用，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/4752595/

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