我正在尝试在 OpenGL 中程序生成一个充满星星的背景。
我采用的方法是创建一个带有立方体贴图纹理的天空盒。立方体贴图纹理的每一面基本上由一个 2048x2048 的黑色图像组成,其中随机选择的纹素设置为白色。结果如下:
我不确定从图像上看它有多明显,但是当围绕一个非常明显的盒子形状移动时,可以看出靠近盒子边缘的星星看起来越来越小,而且越来越靠近。我怎样才能防止这种情况?我是否需要放弃天空盒方法并使用类似天空球的东西?
编辑:这是我将立方体贴图映射到天空的方式。
// Create and bind texture.
glGenTextures(1, &texture_);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_CUBE_MAP, texture_);
for (unsigned int i = 0; i < 6; ++i) {
std::vector<std::uint8_t> image = generateTexture(TEXTURE_WIDTH, TEXTURE_HEIGHT);
glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, 0, GL_RGB, TEXTURE_WIDTH, TEXTURE_HEIGHT,
0, GL_RGB, GL_UNSIGNED_BYTE, image.data());
}
// Set texture parameters.
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);
下面是
generateTexture
函数的定义:std::vector<std::uint8_t> Stars::generateTexture(GLsizei width, GLsizei height) {
std::vector<std::uint8_t> image(static_cast<std::size_t>(3 * width * height));
add_stars(image, NUM_STARS);
return image;
}
void Stars::add_stars(std::vector<std::uint8_t>& image, unsigned int nStars) {
std::default_random_engine eng;
std::uniform_int_distribution<std::size_t> dist(0, image.size() / 3 - 1);
while (nStars--) {
std::size_t index = 3 * dist(eng);
image[index++] = 255;
image[index++] = 255;
image[index++] = 255;
}
}
EDIT2:这是用于渲染天空的绘制函数。
void Stars::draw(const Camera& camera) const {
// Skybox will be rendered last. In order to ensure that the stars are rendered at the back of
// the scene, the depth buffer is filled with values of 1.0 for the skybox -- this is done in
// the vertex shader. We need to make sure that the skybox passes the depth te3t with values
// less that or equal to the depth buffer.
glDepthFunc(GL_LEQUAL);
program_.enable();
// Calculate view-projection matrix and set the corresponding uniform. The view matrix must be
// stripped of translation components so that the skybox follows the camera.
glm::mat4 view = glm::mat4(glm::mat3(camera.viewMatrix()));
glm::mat4 projection = camera.projectionMatrix();
glm::mat4 VP = projection * view;
glUniformMatrix4fv(program_.uniformLocation("VP"), 1, GL_FALSE, glm::value_ptr(VP));
// Bind buffer objects and texture to current context and draw.
glBindVertexArray(vao_);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo_);
glBindTexture(GL_TEXTURE_CUBE_MAP, texture_);
glDrawElements(GL_TRIANGLES, static_cast<GLsizei>(INDICES.size()), GL_UNSIGNED_INT,
reinterpret_cast<GLvoid *>(0));
glBindVertexArray(0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
glBindTexture(GL_TEXTURE_CUBE_MAP, 0);
program_.disable();
glDepthFunc(GL_LESS);
}
最佳答案
x=2.0*Random()-1.0; // <-1,+1>
y=2.0*Random()-1.0; // <-1,+1>
z=2.0*Random()-1.0; // <-1,+1>
所以只需计算 vector
(x,y,z)
的长度并将坐标除以它。 立方体的每一边都由平面定义,因此找到从
(0,0,0)
转换到笛卡尔星位置和平面的光线的交集。取与 (0,0,0)
距离最短的交点,并将其用作最终的星星位置。实现可能是这样的 OpenGL&C++ 代码:
glClearColor(0.0,0.0,0.0,0.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
int i,n=10000;
float a,b,x,y,z;
//RandSeed=8123456789;
n=obj.pnt.num; // triangulated sphere point list
glDepthFunc(GL_LEQUAL);
glEnable(GL_BLEND);
glBlendFunc(GL_ONE,GL_ONE);
glPointSize(2.0);
glBegin(GL_POINTS);
for (i=0;i<n;i++)
{
// equidistant points instead of random to test this
x=obj.pnt[i].p[0];
y=obj.pnt[i].p[1];
z=obj.pnt[i].p[2];
/*
// random star spherical position
a=2.0*M_PI*Random();
b=M_PI*(Random()-0.5);
// spherical 2 cartessian r=1;
x=cos(a)*cos(b);
y=sin(a)*cos(b);
z= sin(b);
*/
// redish sphere map
glColor3f(0.6,0.3,0.0); glVertex3f(x,y,z);
// cube half size=1 undistort // using similarities like: yy/xx = y/x
if ((fabs(x)>=fabs(y))&&(fabs(x)>=fabs(z))){ y/=x; z/=x; if (x>=0) x=1.0; else x=-1.0; }
else if ((fabs(y)>=fabs(x))&&(fabs(y)>=fabs(z))){ x/=y; z/=y; if (y>=0) y=1.0; else y=-1.0; }
else if ((fabs(z)>=fabs(x))&&(fabs(z)>=fabs(y))){ x/=z; y/=z; if (z>=0) z=1.0; else z=-1.0; }
// bluish cube map
glColor3f(0.0,0.3,0.6); glVertex3f(x,y,z);
}
glEnd();
glPointSize(1.0);
glDisable(GL_BLEND);
glFlush();
SwapBuffers(hdc);
看起来它应该在这里预览(混合球体/立方体贴图):
虽然看起来有洞但没有洞(这可能是一些混合错误),如果我禁用球体贴图渲染,那么映射中就没有可见的洞或扭曲。
用于测试的球体三角剖分
mesh obj
取自此处:[Edit1] 是的,有一个愚蠢的混合错误
我修复了代码......但问题仍然存在。这个映射是否正常工作并不重要,更新后的代码结果应该在这里:
所以只需将代码调整为您的纹理生成器......
[Edit2] 随机星星
glClearColor(0.0,0.0,0.0,0.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
int i;
float x,y,z,d;
RandSeed=8123456789;
glDepthFunc(GL_LEQUAL);
glEnable(GL_BLEND);
glBlendFunc(GL_ONE,GL_ONE);
glPointSize(2.0);
glBegin(GL_POINTS);
for (i=0;i<1000;i++)
{
// uniform random cartesian stars inside cube
x=(2.0*Random())-1.0;
y=(2.0*Random())-1.0;
z=(2.0*Random())-1.0;
// project on unit sphere
d=sqrt((x*x)+(y*y)+(z*z));
if (d<1e-3) { i--; continue; }
d=1.0/d;
x*=d; y*=d; z*=d;
// redish sphere map
glColor3f(0.6,0.3,0.0); glVertex3f(x,y,z);
// cube half size=1 undistort using similarities like: y/x = y'/x'
if ((fabs(x)>=fabs(y))&&(fabs(x)>=fabs(z))){ y/=x; z/=x; if (x>=0) x=1.0; else x=-1.0; }
else if ((fabs(y)>=fabs(x))&&(fabs(y)>=fabs(z))){ x/=y; z/=y; if (y>=0) y=1.0; else y=-1.0; }
else if ((fabs(z)>=fabs(x))&&(fabs(z)>=fabs(y))){ x/=z; y/=z; if (z>=0) z=1.0; else z=-1.0; }
// bluish cube map
glColor3f(0.0,0.3,0.6); glVertex3f(x,y,z);
}
glEnd();
glPointSize(1.0);
glDisable(GL_BLEND);
glFlush();
SwapBuffers(hdc);
这里混合展位(1000 颗星):
而这里只有立方体贴图(10000颗星)
[Edit3] Blend 问题解决了
这是由于忘记了
fabs
这里固定代码,在投影过程中由于 Z-fighting 和偶尔更改某些坐标的符号引起的: glClearColor(0.0,0.0,0.0,0.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
int i;
float x,y,z,d;
RandSeed=8123456789;
glDepthFunc(GL_ALWAYS);
// glDepthFunc(GL_LEQUAL);
glEnable(GL_BLEND);
glBlendFunc(GL_ONE,GL_ONE);
glPointSize(2.0);
glBegin(GL_POINTS);
for (i=0;i<25000;i++)
{
// uniform random cartesian stars inside cube
x=(2.0*Random())-1.0;
y=(2.0*Random())-1.0;
z=(2.0*Random())-1.0;
// project on unit sphere
d=sqrt((x*x)+(y*y)+(z*z));
if (d<1e-3) { i--; continue; }
d=1.0/d;
x*=d; y*=d; z*=d;
// redish sphere map
glColor3f(0.6,0.3,0.0); glVertex3f(x,y,z);
// cube half size=1 undistort using similarities like: y/x = y'/x'
if ((fabs(x)>=fabs(y))&&(fabs(x)>=fabs(z))){ y/=fabs(x); z/=fabs(x); if (x>=0) x=1.0; else x=-1.0; }
else if ((fabs(y)>=fabs(x))&&(fabs(y)>=fabs(z))){ x/=fabs(y); z/=fabs(y); if (y>=0) y=1.0; else y=-1.0; }
else if ((fabs(z)>=fabs(x))&&(fabs(z)>=fabs(y))){ x/=fabs(z); y/=fabs(z); if (z>=0) z=1.0; else z=-1.0; }
// bluish cube map
glColor3f(0.0,0.3,0.6); glVertex3f(x,y,z);
}
glEnd();
glPointSize(1.0);
glDisable(GL_BLEND);
glFlush();
SwapBuffers(hdc);
这里的混合结果最终颜色应该是这样的,所以从
(0,0,0)
观看时,球体和立方星完美重叠(白色):关于c++ - 用天空盒程序生成星星,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/38061481/