具有高多边形网格的OpenGL 3D光线拾取 [英] OpenGL 3D-raypicking with high poly meshes
问题描述
如何使用包含高多边形网格的模型在3d场景中实现3d光线拾取?
How to implement 3d raypicking in an 3d scene with models that contain high poly meshes?
遍历所有三角形以执行三角形线相交测试需要太多时间.我知道存在octree等方法，应该可以将它们用于场景中的模型，但是我不知道如何在网格级别使用这些概念.但是，如果您在网格级别使用八叉树，那么应该如何解决超出八叉树体积边界的多边形问题呢?
It takes too much time to iterate over all triangles to perform a triangle-line-intersection test. I know that there exist methods like octree etc. and it should be possible to use these for the models in the scene, but I do not know how I should use these concepts at mesh-level. But if you use an octree at mesh-level, how should one cover problems with polygons, that exceed the boundaries of the octree volumes?
您是否对哪种方法适合或推荐用于实时OpenGl应用程序的具有高多边形模型的3d射线相交?
Do you have any advice which method is suitable or recommended for 3d ray-intersections with high poly models for real-time OpenGl applications?
推荐答案
对于光线拾取渲染对象(如通过鼠标)，最好的选择是使用已经渲染的缓冲区，因为与ray相比，读取它们的成本非常低复杂场景下的路口测试.想法是将每个可拾取的渲染对象渲染为每个您需要的有关它们的信息的单独缓冲区，例如:
For ray picking rendered objects (like by mouse) the best option is to use the already rendered buffers as there is very little cost of reading them in comparison to ray intersection tests on complex scene. The idea is to render each pick-able rendered object to separate buffer per each info you need about them for example like this:
-
深度缓冲区
这将为您提供射线与对象相交的 3D 位置.
this will give you the 3D position of the ray intersection with object.
模板缓冲区
如果每个对象使用其 ID (或其在对象列表中的索引)渲染到模具中，则可以直接获取选取的对象.
if each object rendered to stencil with its ID (or its index in object list) then you can get the picked object directly.
其他
还有辅助颜色附件和FBO.因此，您可以添加其他任何东西，例如法线向量或任何您需要的东西.
there are also secondary color attachments and FBO's out there. So you can add any other stuff like normal vector or what ever you need.
如果编码正确，那么所有这些都只会稍微降低性能(甚至根本不会降低)，因为您不需要计算任何内容，只需每个缓冲区每个片段一次写入即可.
If coded right all of this will reduce performance only slightly (even not at all) as you do not need to compute anything its just a single write per fragment per buffer.
选择本身很容易，您只需从所需的所有缓冲区中读取相应的像素并将其转换为所需的格式即可.
The picking itself is easy you just read the corresponding pixel from all the buffers you need and convert to wanted format.
下面是使用固定管道(无着色器)的简单 C ++/VCL 示例...
Here simple C++/VCL example using fixed pipeline (no shaders)...
//---------------------------------------------------------------------------
#include <vcl.h>
#include <math.h>
#pragma hdrstop
#include "Unit1.h"
#include "gl_simple.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
void matrix_mul_vector(double *c,double *a,double *b,double w=1.0)
{
double q[3];
q[0]=(a[ 0]*b[0])+(a[ 4]*b[1])+(a[ 8]*b[2])+(a[12]*w);
q[1]=(a[ 1]*b[0])+(a[ 5]*b[1])+(a[ 9]*b[2])+(a[13]*w);
q[2]=(a[ 2]*b[0])+(a[ 6]*b[1])+(a[10]*b[2])+(a[14]*w);
for(int i=0;i<3;i++) c[i]=q[i];
}
//---------------------------------------------------------------------------
class glMouse
{
public:
int sx,sy; // framebuffer position [pixels]
double pos[3]; // [GCS] ray end coordinate (or z_far)
double beg[3]; // [GCS] ray start (z_near)
double dir[3]; // [GCS] ray direction
double depth; // [GCS] perpendicular distance to camera
WORD id; // selected object id
double x0,y0,xs,ys,zFar,zNear; // viewport and projection
double *eye; // camera direct matrix pointer
double fx,fy; // perspective scales
glMouse(){ eye=NULL; for (int i=0;i<3;i++) { pos[i]=0.0; beg[i]=0.0; dir[i]=0.0; } id=0; x0=0.0; y0=0.0; xs=0.0; ys=0.0; fx=0.0; fy=0.0; depth=0.0; }
glMouse(glMouse& a){ *this=a; };
~glMouse(){};
glMouse* operator = (const glMouse *a) { *this=*a; return this; };
// glMouse* operator = (const glMouse &a) { ...copy... return this; };
void resize(double _x0,double _y0,double _xs,double _ys,double *_eye)
{
double per[16];
x0=_x0; y0=_y0; xs=_xs; ys=_ys; eye=_eye;
glGetDoublev(GL_PROJECTION_MATRIX,per);
zFar =0.5*per[14]*(1.0-((per[10]-1.0)/(per[10]+1.0)));
zNear=zFar*(per[10]+1.0)/(per[10]-1.0);
fx=per[0];
fy=per[5];
}
void pick(double x,double y) // test screen x,y [pixels] position
{
int i;
double l;
GLfloat _z;
GLint _id;
sx=x; sy=ys-1.0-y;
// read depth z and linearize
glReadPixels(sx,sy,1,1,GL_DEPTH_COMPONENT,GL_FLOAT,&_z);// read depth value
depth=_z; // logarithmic
depth=(2.0*depth)-1.0; // logarithmic NDC
z=(2.0*zNear*zFar)/(zFar+zNear-(z*(zFar-zNear))); // linear <zNear,zFar>
// read object ID
glReadPixels(sx,sy,1,1,GL_STENCIL_INDEX,GL_INT,&_id); // read stencil value
id=_id;
// win [pixel] -> GL NDC <-1,+1>
x= (2.0*(x-x0)/xs)-1.0;
y=1.0-(2.0*(y-y0)/ys);
// ray start GL camera [LCS]
beg[2]=-zNear;
beg[1]=(-beg[2]/fy)*y;
beg[0]=(-beg[2]/fx)*x;
// ray direction GL camera [LCS]
for (l=0.0,i=0;i<3;i++) l+=beg[i]*beg[i]; l=1.0/sqrt(l);
for (i=0;i<3;i++) dir[0]=beg[0]*l;
// ray end GL camera [LCS]
pos[2]=-depth;
pos[1]=(-pos[2]/fy)*y;
pos[0]=(-pos[2]/fx)*x;
// convert to [GCS]
matrix_mul_vector(beg,eye,beg);
matrix_mul_vector(pos,eye,pos);
matrix_mul_vector(dir,eye,dir,0.0);
}
};
//---------------------------------------------------------------------------
// camera & mouse
double eye[16],ieye[16]; // direct view,inverse view and perspective matrices
glMouse mouse;
// objects
struct object
{
WORD id; // unique non zero ID
double m[16]; // direct model matrix
object(){}; object(object& a){ *this=a; }; ~object(){}; object* operator = (const object *a) { *this=*a; return this; }; /*object* operator = (const object &a) { ...copy... return this; };*/
};
const int objs=7;
object obj[objs];
// textures
GLuint txr=-1;
//---------------------------------------------------------------------------
void matrix_inv(double *a,double *b) // a[16] = Inverse(b[16])
{
double x,y,z;
// transpose of rotation matrix
a[ 0]=b[ 0];
a[ 5]=b[ 5];
a[10]=b[10];
x=b[1]; a[1]=b[4]; a[4]=x;
x=b[2]; a[2]=b[8]; a[8]=x;
x=b[6]; a[6]=b[9]; a[9]=x;
// copy projection part
a[ 3]=b[ 3];
a[ 7]=b[ 7];
a[11]=b[11];
a[15]=b[15];
// convert origin: new_pos = - new_rotation_matrix * old_pos
x=(a[ 0]*b[12])+(a[ 4]*b[13])+(a[ 8]*b[14]);
y=(a[ 1]*b[12])+(a[ 5]*b[13])+(a[ 9]*b[14]);
z=(a[ 2]*b[12])+(a[ 6]*b[13])+(a[10]*b[14]);
a[12]=-x;
a[13]=-y;
a[14]=-z;
}
//---------------------------------------------------------------------------
void gl_draw()
{
int i; object *o;
double a;
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT );
glEnable(GL_CULL_FACE);
glEnable(GL_DEPTH_TEST);
glEnable(GL_STENCIL_TEST);
glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
glStencilMask(0xFFFF); // Write to stencil buffer
glStencilFunc(GL_ALWAYS,0,0xFFFF); // Set any stencil to 0
for (o=obj,i=0;i<objs;i++,o++)
{
glMatrixMode(GL_MODELVIEW);
glLoadMatrixd(ieye);
glMultMatrixd(o->m);
glStencilFunc(GL_ALWAYS,o->id,0xFFFF); // Set any stencil to object ID
vao_draw();
}
glStencilFunc(GL_ALWAYS,0,0xFFFF); // Set any stencil to 0
glDisable(GL_STENCIL_TEST); // no need fot testing
// render mouse
glMatrixMode(GL_MODELVIEW);
glLoadMatrixd(ieye);
a=0.1*mouse.depth;
glColor3f(0.0,1.0,0.0);
glBegin(GL_LINES);
glVertex3d(mouse.pos[0]+a,mouse.pos[1],mouse.pos[2]);
glVertex3d(mouse.pos[0]-a,mouse.pos[1],mouse.pos[2]);
glVertex3d(mouse.pos[0],mouse.pos[1]+a,mouse.pos[2]);
glVertex3d(mouse.pos[0],mouse.pos[1]-a,mouse.pos[2]);
glVertex3d(mouse.pos[0],mouse.pos[1],mouse.pos[2]+a);
glVertex3d(mouse.pos[0],mouse.pos[1],mouse.pos[2]-a);
glEnd();
Form1->Caption=AnsiString().sprintf("%.3lf , %.3lf , %.3lf : %u",mouse.pos[0],mouse.pos[1],mouse.pos[2],mouse.id);
// debug buffer views
if ((Form1->ck_depth->Checked)||(Form1->ck_stencil->Checked))
{
glDisable(GL_DEPTH_TEST);
glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D,txr);
GLfloat *f=new GLfloat[xs*ys],z;
if (Form1->ck_depth ->Checked)
{
glReadPixels(0,0,xs,ys,GL_DEPTH_COMPONENT,GL_FLOAT,f);
for (i=0;i<xs*ys;i++) f[i]=1.0-(2.0*mouse.zNear)/(mouse.zFar+mouse.zNear-(((2.0*f[i])-1.0)*(mouse.zFar-mouse.zNear)));
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, xs, ys, 0, GL_RED, GL_FLOAT, f);
}
if (Form1->ck_stencil->Checked)
{
glReadPixels(0,0,xs,ys,GL_STENCIL_INDEX,GL_FLOAT,f);
for (i=0;i<xs*ys;i++) f[i]/=float(objs);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, xs, ys, 0, GL_GREEN, GL_FLOAT, f);
}
delete[] f;
glColor3f(1.0,1.0,1.0);
glBegin(GL_QUADS);
glTexCoord2f(1.0,0.0); glVertex2f(+1.0,-1.0);
glTexCoord2f(1.0,1.0); glVertex2f(+1.0,+1.0);
glTexCoord2f(0.0,1.0); glVertex2f(-1.0,+1.0);
glTexCoord2f(0.0,0.0); glVertex2f(-1.0,-1.0);
glEnd();
glMatrixMode(GL_PROJECTION);
glPopMatrix();
glDisable(GL_TEXTURE_2D);
glEnable(GL_DEPTH_TEST);
}
glFlush();
SwapBuffers(hdc);
}
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner):TForm(Owner)
{
int i;
object *o;
gl_init(Handle);
vao_init();
// init textures
glGenTextures(1,&txr);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D,txr);
glPixelStorei(GL_UNPACK_ALIGNMENT, 4);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,GL_NEAREST);
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE,GL_COPY);
glDisable(GL_TEXTURE_2D);
// init objects
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(-1.5,4.7,-8.0);
for (o=obj,i=0;i<objs;i++,o++)
{
o->id=i+1; // unique non zero ID
glGetDoublev(GL_MODELVIEW_MATRIX,o->m);
glRotatef(360.0/float(objs),0.0,0.0,1.0);
glTranslatef(-3.0,0.0,0.0);
}
for (o=obj,i=0;i<objs;i++,o++)
{
glLoadMatrixd(o->m);
glRotatef(180.0*Random(),Random(),Random(),Random());
glGetDoublev(GL_MODELVIEW_MATRIX,o->m);
}
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormDestroy(TObject *Sender)
{
glDeleteTextures(1,&txr);
gl_exit();
vao_exit();
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormResize(TObject *Sender)
{
gl_resize(ClientWidth,ClientHeight);
// obtain/init matrices
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0,0,-15.0);
glGetDoublev(GL_MODELVIEW_MATRIX,ieye);
matrix_inv(eye,ieye);
mouse.resize(0,0,xs,ys,eye);
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormPaint(TObject *Sender)
{
gl_draw();
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Timer1Timer(TObject *Sender)
{
gl_draw();
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormMouseWheel(TObject *Sender, TShiftState Shift, int WheelDelta, TPoint &MousePos, bool &Handled)
{
GLfloat dz=2.0;
if (WheelDelta<0) dz=-dz;
glMatrixMode(GL_MODELVIEW);
glLoadMatrixd(ieye);
glTranslatef(0,0,dz);
glGetDoublev(GL_MODELVIEW_MATRIX,ieye);
matrix_inv(eye,ieye);
gl_draw();
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormMouseMove(TObject *Sender, TShiftState Shift, int X, int Y)
{
mouse.pick(X,Y);
}
//---------------------------------------------------------------------------
void __fastcall TForm1::ck_depthClick(TObject *Sender)
{
gl_draw();
}
//---------------------------------------------------------------------------
此处是左RGB，深度，模具的预览:
此处捕获的GIF:
前3个数字是[GCS]中所拾取像素的 3D 位置，标题中的最后一个数字是所拾取的 ID ，其中0表示没有对象.
the first 3 numbers are the 3D position of picked pixel in [GCS] and the last number in caption is the picked ID where 0 means no object.
该示例从此处使用gl_simple,h:
您可以忽略VCL，因为它并不重要，只需将事件移植到您的环境中即可.
You can ignore the VCL stuff as its not important just port the events to your environment...
那该怎么办:
-
渲染
您需要将模板缓冲区添加到您的 GL 窗口像素格式，因此在我的情况下，我只需添加:
You need add stencil buffer to your GL window pixel format so in my case I just add:
pfd.cStencilBits = 16;
将
从gl_simple.h转换为gl_init()功能.还将其位添加到glClear中，并将每个对象模具设置为其 ID ，就像我在gl_draw()中所做的那样.
into gl_init() function from gl_simple.h. Also add its bit into glClear and set each objects stencil to its ID Like I did in gl_draw().
领取
我写了一个小的glMouse类来完成所有繁重的工作.每次更改透视图，视图或视口时，均调用其glMouse::resize函数.这将准备以后计算所需的所有常数.当心它需要直接的摄像头/视图矩阵！！！
I wrote a small glMouse class that do all the heavy lifting. On each change of perspective, view, or viewport call its glMouse::resize function. That will prepare all the constants needed for the computations later. Beware it needs direct camera/view matrix !!!
现在，每次鼠标移动(或单击或执行任何操作)时，调用glMouse::pick函数，然后使用类似id的结果，该结果将返回使用[GCS])中的 3D 坐标.
Now on each mouse movement (or click or whatever) call the glMouse::pick function and then use the results like id which will return the ID picked object was rendered with or pos which is the 3D coordinate in global world coordinates ([GCS]) of the ray object intersection.
该功能仅读取深度和模板缓冲区.像这样线性化深度:
The function just read the depth and stencil buffers. Linearize depth like here:
并在[GCS]中计算射线beg,dir,pos,depth.
普通
您有2个选择，可以将法线渲染为另一个缓冲区，这是最简单，最精确的.或者，读取一个像素周围2个或更多相邻像素的读取深度，计算其3D位置.通过使用叉积计算，可以计算出法线和平均值(如果需要).但这会导致边缘出现伪像.
You got 2 options either render your normal as another buffer which is the simplest and most precise. Or read depths of 2 or more neighboring pixels around picked one compute their 3D positions. From that using cross product compute you normal(s) and average if needed. But this can lead to artifacts on edges.
如注释中所述，为了提高准确性，您应该使用线性深度缓冲区，而不是像这样的线性对数:
As mentioned in the comments to boost accuracy you should use linear depth buffer instead of linearized logarithmic like this:
顺便说一句，我在这里使用了相同的技术(在基于GDI的SW等距渲染中):
Btw I used the same technique in here (in GDI based SW isometric render):
这篇关于具有高多边形网格的OpenGL 3D光线拾取的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
