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[英]OpenGL appears to be using (far too aggressive) frustum culling which I can't see how to modify
[英]OpenGL - Frustum not culling polygons beyond far plane
我已经实现了视锥剔除,并正在检查边界框与视锥平面的交集。 我添加了暂停视锥更新的功能,该功能使我可以查看视锥剔除是否已正常进行。 当我暂停后转身时,在我身后和左右两侧都没有任何东西呈现,它们逐渐变细,就像您期望的那样。 超出剪辑距离(远平面),它们仍会渲染,并且我不确定我的视锥更新或边界框检查代码是否有问题,或者我使用的矩阵错误还是什么。 当我在投影矩阵中将距离设置为3000.0f时,它仍然说边界框已经过了截锥体,但情况并非如此。
这是我创建模型视图矩阵的地方:
projectionMatrix = glm::perspective(newFOV, 4.0f / 3.0f, 0.1f, 3000.0f);
viewMatrix = glm::mat4(1.0);
viewMatrix = glm::scale(viewMatrix, glm::vec3(1.0, 1.0, -1.0));
viewMatrix = glm::rotate(viewMatrix, anglePitch, glm::vec3(1.0, 0.0, 0.0));
viewMatrix = glm::rotate(viewMatrix, angleYaw, glm::vec3(0.0, 1.0, 0.0));
viewMatrix = glm::translate(viewMatrix, glm::vec3(-x, -y, -z));
modelViewProjectiomMatrix = projectionMatrix * viewMatrix;
之所以在Z方向上按-1缩放比例,是因为级别被设计为使用DirectX渲染,所以我将Z方向反转。
这是我更新视锥的地方:
void CFrustum::calculateFrustum()
{
glm::mat4 mat = camera.getModelViewProjectionMatrix();
// Calculate the LEFT side
m_Frustum[LEFT][A] = (mat[0][3]) + (mat[0][0]);
m_Frustum[LEFT][B] = (mat[1][3]) + (mat[1][0]);
m_Frustum[LEFT][C] = (mat[2][3]) + (mat[2][0]);
m_Frustum[LEFT][D] = (mat[3][3]) + (mat[3][0]);
// Calculate the RIGHT side
m_Frustum[RIGHT][A] = (mat[0][3]) - (mat[0][0]);
m_Frustum[RIGHT][B] = (mat[1][3]) - (mat[1][0]);
m_Frustum[RIGHT][C] = (mat[2][3]) - (mat[2][0]);
m_Frustum[RIGHT][D] = (mat[3][3]) - (mat[3][0]);
// Calculate the TOP side
m_Frustum[TOP][A] = (mat[0][3]) - (mat[0][1]);
m_Frustum[TOP][B] = (mat[1][3]) - (mat[1][1]);
m_Frustum[TOP][C] = (mat[2][3]) - (mat[2][1]);
m_Frustum[TOP][D] = (mat[3][3]) - (mat[3][1]);
// Calculate the BOTTOM side
m_Frustum[BOTTOM][A] = (mat[0][3]) + (mat[0][1]);
m_Frustum[BOTTOM][B] = (mat[1][3]) + (mat[1][1]);
m_Frustum[BOTTOM][C] = (mat[2][3]) + (mat[2][1]);
m_Frustum[BOTTOM][D] = (mat[3][3]) + (mat[3][1]);
// Calculate the FRONT side
m_Frustum[FRONT][A] = (mat[0][3]) + (mat[0][2]);
m_Frustum[FRONT][B] = (mat[1][3]) + (mat[1][2]);
m_Frustum[FRONT][C] = (mat[2][3]) + (mat[2][2]);
m_Frustum[FRONT][D] = (mat[3][3]) + (mat[3][2]);
// Calculate the BACK side
m_Frustum[BACK][A] = (mat[0][3]) - (mat[0][2]);
m_Frustum[BACK][B] = (mat[1][3]) - (mat[1][2]);
m_Frustum[BACK][C] = (mat[2][3]) - (mat[2][2]);
m_Frustum[BACK][D] = (mat[3][3]) - (mat[3][2]);
// Normalize all the sides
NormalizePlane(m_Frustum, LEFT);
NormalizePlane(m_Frustum, RIGHT);
NormalizePlane(m_Frustum, TOP);
NormalizePlane(m_Frustum, BOTTOM);
NormalizePlane(m_Frustum, FRONT);
NormalizePlane(m_Frustum, BACK);
}
最后,在检查边框的地方:
bool CFrustum::BoxInFrustum( float x, float y, float z, float x2, float y2, float z2)
{
// Go through all of the corners of the box and check then again each plane
// in the frustum. If all of them are behind one of the planes, then it most
// like is not in the frustum.
for(int i = 0; i < 6; i++ )
{
if(m_Frustum[i][A] * x + m_Frustum[i][B] * y + m_Frustum[i][C] * z + m_Frustum[i][D] > 0) continue;
if(m_Frustum[i][A] * x2 + m_Frustum[i][B] * y + m_Frustum[i][C] * z + m_Frustum[i][D] > 0) continue;
if(m_Frustum[i][A] * x + m_Frustum[i][B] * y2 + m_Frustum[i][C] * z + m_Frustum[i][D] > 0) continue;
if(m_Frustum[i][A] * x2 + m_Frustum[i][B] * y2 + m_Frustum[i][C] * z + m_Frustum[i][D] > 0) continue;
if(m_Frustum[i][A] * x + m_Frustum[i][B] * y + m_Frustum[i][C] * z2 + m_Frustum[i][D] > 0) continue;
if(m_Frustum[i][A] * x2 + m_Frustum[i][B] * y + m_Frustum[i][C] * z2 + m_Frustum[i][D] > 0) continue;
if(m_Frustum[i][A] * x + m_Frustum[i][B] * y2 + m_Frustum[i][C] * z2 + m_Frustum[i][D] > 0) continue;
if(m_Frustum[i][A] * x2 + m_Frustum[i][B] * y2 + m_Frustum[i][C] * z2 + m_Frustum[i][D] > 0) continue;
// If we get here, it isn't in the frustum
return false;
}
// Return a true for the box being inside of the frustum
return true;
}
我注意到了几件事,尤其是关于如何设置投影矩阵的事情。 对于初学者,除非您使用某种包装器或怪异的api,否则gluProject不会返回值。 gluLookAt经常使用。
接下来,假设缩放,旋转和平移功能旨在更改模型视图矩阵,则需要颠倒它们的顺序。 OpenGL实际上并没有移动对象。 而是有效地移动原点,并使用新定义的<0,0,0>渲染每个对象。 因此,您可以“移动”到要渲染的位置,然后根据需要旋转轴,然后拉伸网格。
至于裁剪问题,您可能希望给glClipPlane()一个好的外观。 如果一切工作大多 ,但似乎有些舍入误差,尝试在你的观点改变了近裁剪平面(,,,)函数从0.1到1.0(较小的值往往会乱用Z缓冲)。
我看到了许多不熟悉的语法,所以我认为您正在使用某种包装器。 但是这是我使用的GL项目中的一些(Qt)代码片段。 可能会帮助,邓诺:
//This gets called during resize, as well as once during initialization
void GLWidget::resizeGL(int width, int height) {
int side = qMin(width, height);
padX = (width-side)/2.0;
padY = (height-side)/2.0;
glViewport(padX, padY, side, side);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(60.0, 1.0, 1.0, 2400.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
//This fragment gets called at the top of every paint event:
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glPushMatrix();
glLightfv(GL_LIGHT0, GL_POSITION, FV0001);
camMain.stepVars();
gluLookAt(camMain.Pos[0],camMain.Pos[1],camMain.Pos[2],
camMain.Aim[0],camMain.Aim[1],camMain.Aim[2],
0.0,1.0,0.0);
glPolygonMode(GL_FRONT_AND_BACK, drawMode);
//And this fragment represents a typical draw event
void GLWidget::drawFleet(tFleet* tIn) {
if (tIn->firstShip != 0){
glPushMatrix();
glTranslatef(tIn->Pos[0], tIn->Pos[1], tIn->Pos[2]);
glRotatef(tIn->Yaw, 0.0, 1.0, 0.0);
glRotatef(tIn->Pitch,0,0,1);
drawShip(tIn->firstShip);
glPopMatrix();
}
}
我正在假设您是GL的新手,所以如果我有点腐,我深表歉意。
我有同样的问题。
给定Vinny Rose的答案,我检查了创建归一化平面的函数,并发现了错误。
这是更正的版本,其中不正确的计算已被注释掉:
plane plane_normalized(float A, float B, float C, float D) {
// Wrong, this is not a 4D vector
// float nf = 1.0f / sqrtf(A * A + B * B + C * C + D * D);
// Correct
float nf = 1.0f / sqrtf(A * A + B * B + C * C);
return (plane) {{
nf * A,
nf * B,
nf * C,
nf * D
}};
}
我的猜测是您的NormalizePlane
函数会执行类似的操作。
规范化的目的是使飞机具有Hessian范式,以便我们可以轻松进行半空间测试。 如果像对待四维矢量一样对平面进行归一化,则法线方向[A,B,C]仍然正确,但偏移D却不正确。
我认为在针对顶部,底部,左侧和右侧的平面测试点时,您会获得正确的结果,因为它们通过了原点,并且近平面可能足够靠近而不会引起注意。 (边界球测试将失败。)
当我恢复正确的归一化时,平截头体剔除对我来说工作正常。
我想这是正在发生的事情:远端平面的定义正确,但是在我的测试中,该平面的D值太小了。 因此,物体被接受为位于远平面的正确一侧,因为数学运算迫使远平面实际上比您想要的远得多。
尝试不同的方法:(http://www.lighthouse3d.com/tutorials/view-frustum-culling/geometric-approach-extracting-the-planes/)
float tang = tanf(fov * PI / 360.0f);
float nh = near * tang; // near height
float nw = nh * aspect; // near width
float fh = far * tang; // far height
float fw = fh * aspect; // far width
glm::vec3 p,nc,fc,X,Y,Z,Xnw,Ynh;
//camera position
p = glm::vec3(viewMatrix[3][0],viewMatrix[3][1],viewMatrix[3][2]);
// the left vector
glm::vec3 X = glm::vec3(viewMatrix[0][0], viewMatrix[1][0], viewMatrix[2][0]);
// the up vector
glm::vec3 Y = glm::vec3(viewMatrix[0][1], viewMatrix[1][1], viewMatrix[2][1]);
// the look vector
glm::vec3 Z = glm::vec3(viewMatrix[0][2], viewMatrix[1][2], viewMatrix[2][2]);
nc = p - Z * near; // center of the near plane
fc = p - Z * far; // center of the far plane
// the distance to get to the left or right edge of the near plane from nc
Xnw = X * nw;
// the distance to get to top or bottom of the near plane from nc
Ynh = Y * nh;
// the distance to get to the left or right edge of the far plane from fc
Xfw = X * fw;
// the distance to get to top or bottom of the far plane from fc
Yfh = Y * fh;
ntl = nc + Ynh - Xnw; // "near top left"
ntr = nc + Ynh + Xnw; // "near top right" and so on
nbl = nc - Ynh - Xnw;
nbr = nc - Ynh + Xnw;
ftl = fc + Yfh - Xfw;
ftr = fc + Yfh + Xfw;
fbl = fc - Yfh - Xfw;
fbr = fc - Yfh + Xfw;
m_Frustum[TOP] = planeWithPoints(ntr,ntl,ftl);
m_Frustum[BOTTOM] = planeWithPoints(nbl,nbr,fbr);
m_Frustum[LEFT] = planeWithPoints(ntl,nbl,fbl);
m_Frustum[RIGHT] = planeWithPoints(nbr,ntr,fbr);
m_Frustum[FRONT] = planeWithPoints(ntl,ntr,nbr);
m_Frustum[BACK] = planeWithPoints(ftr,ftl,fbl);
// Normalize all the sides
NormalizePlane(m_Frustum, LEFT);
NormalizePlane(m_Frustum, RIGHT);
NormalizePlane(m_Frustum, TOP);
NormalizePlane(m_Frustum, BOTTOM);
NormalizePlane(m_Frustum, FRONT);
NormalizePlane(m_Frustum, BACK);
然后,planeWithPoints将类似于:
planeWithPoints(glm::vec3 a, glm::vec3 b, glm::vec3 c){
double A = a.y * (b.z - c.z) + b.y * (c.z - a.z) + c.y * (a.z - b.z);
double B = a.z * (b.x - c.x) + b.z * (c.x - a.x) + c.z * (a.x - b.x);
double C = a.x * (b.y - c.y) + b.x * (c.y - a.y) + c.x * (a.y - b.y);
double D = -(a.x * (b.y * c.z - c.y * b.z) + b.x * (c.y * a.z - a.y * c.z) + c.x * (a.y * b.z - b.y * a.z));
return glm::vec4(A,B,C,D);
}
我没有测试任何上述内容。 但是如果需要,可以使用原始参考。
上一个答案: 当矩阵由2D数组表示时,OpenGL和GLSL矩阵以列优先顺序存储和访问。 对于GLM,这也是正确的,因为它们遵循GLSL标准。
您需要将您的视锥创建更改为以下内容。
// Calculate the LEFT side (column1 + column4) m_Frustum[LEFT][A] = (mat[3][0]) + (mat[0][0]); m_Frustum[LEFT][B] = (mat[3][1]) + (mat[0][1]); m_Frustum[LEFT][C] = (mat[3][2]) + (mat[0][2]); m_Frustum[LEFT][D] = (mat[3][3]) + (mat[0][3]); // Calculate the RIGHT side (-column1 + column4) m_Frustum[RIGHT][A] = (mat[3][0]) - (mat[0][0]); m_Frustum[RIGHT][B] = (mat[3][1]) - (mat[0][1]); m_Frustum[RIGHT][C] = (mat[3][2]) - (mat[0][2]); m_Frustum[RIGHT][D] = (mat[3][3]) - (mat[0][3]); // Calculate the TOP side (-column2 + column4) m_Frustum[TOP][A] = (mat[3][0]) - (mat[1][0]); m_Frustum[TOP][B] = (mat[3][1]) - (mat[1][1]); m_Frustum[TOP][C] = (mat[3][2]) - (mat[1][2]); m_Frustum[TOP][D] = (mat[3][3]) - (mat[1][3]); // Calculate the BOTTOM side (column2 + column4) m_Frustum[BOTTOM][A] = (mat[3][0]) + (mat[1][0]); m_Frustum[BOTTOM][B] = (mat[3][1]) + (mat[1][1]); m_Frustum[BOTTOM][C] = (mat[3][2]) + (mat[1][2]); m_Frustum[BOTTOM][D] = (mat[3][3]) + (mat[1][3]); // Calculate the FRONT side (column3 + column4) m_Frustum[FRONT][A] = (mat[3][0]) + (mat[2][0]); m_Frustum[FRONT][B] = (mat[3][1]) + (mat[2][1]); m_Frustum[FRONT][C] = (mat[3][2]) + (mat[2][2]); m_Frustum[FRONT][D] = (mat[3][3]) + (mat[2][3]); // Calculate the BACK side (-column3 + column4) m_Frustum[BACK][A] = (mat[3][0]) - (mat[2][0]); m_Frustum[BACK][B] = (mat[3][1]) - (mat[2][1]); m_Frustum[BACK][C] = (mat[3][2]) - (mat[2][2]); m_Frustum[BACK][D] = (mat[3][3]) - (mat[2][3]);
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