用OpenGL绘制椭球时的问题 [英] Issue in drawing ellipsoid with OpenGL
问题描述
这是我用来在带有着色器的OpenGL中创建和绘制椭圆体的代码
this is the code I use to create and draw an ellipsoid with OpenGL with shader
const float _2pi = 2.0f * M_PI;
std::vector<glm::vec3> positions;
std::vector<glm::vec3> normals;
std::vector<glm::vec2> textureCoords;
for(int i = 0; i <= stacks; ++i) {
// V texture coordinate
float V = i / (float)stacks;
float phi = V * M_PI;
for( int j = 0; j <= slices; ++j) {
// U texture coordinate
float U = j / (float)slices;
float theta = U * _2pi;
float X = a * cos(theta) * cos(phi);
float Y = b * cos(theta) * sin(phi);
float Z = c * sin(theta);
positions.push_back( glm::vec3( X, Y, Z) );
normals.push_back( glm::vec3(X, Y, Z) );
textureCoords.push_back( glm::vec2(U, V) );
}
}
// Now generate the index buffer
std::vector<GLuint> indicies;
for(int i=0; i <slices*stacks+slices; ++i) {
indicies.push_back(i);
indicies.push_back(i + slices + 1);
indicies.push_back(i + slices);
indicies.push_back(i + slices + 1);
indicies.push_back(i);
indicies.push_back(i + 1);
}
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
glGenBuffers(4, vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo[0]);
glBufferData(GL_ARRAY_BUFFER, positions.size() * sizeof(glm::vec3), positions.data(), GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, nullptr);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, vbo[1]);
glBufferData(GL_ARRAY_BUFFER, normals.size() * sizeof(glm::vec3), normals.data(), GL_STATIC_DRAW);
glVertexAttribPointer(2, 3, GL_FLOAT, GL_TRUE, 0, nullptr);
glEnableVertexAttribArray(2);
glBindBuffer(GL_ARRAY_BUFFER, vbo[2]);
glBufferData(GL_ARRAY_BUFFER, textureCoords.size() * sizeof(glm::vec2), textureCoords.data(), GL_STATIC_DRAW);
glVertexAttribPointer(8, 2, GL_FLOAT, GL_FALSE, 0, nullptr);
glEnableVertexAttribArray(8);
glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, vbo[3]);
glBufferData( GL_ELEMENT_ARRAY_BUFFER, indicies.size() * sizeof(GLuint), indicies.data(), GL_STATIC_DRAW);
glBindVertexArray(0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
这是我用来渲染它的代码:
while this is the code that I use to render it:
glBindVertexArray(vao);
glEnableVertexAttribArray(0);
if(style == glObject::STYLE::WIREFRAME) glDrawElements(GL_LINES, (slices * stacks + slices) * 6, GL_UNSIGNED_INT, nullptr);
if(style == glObject::STYLE::SOLID) glDrawElements(GL_TRIANGLES, (slices * stacks + slices) * 6, GL_UNSIGNED_INT, nullptr);
glBindVertexArray(0);
这似乎可行，但我遇到了一些问题. 查看图像可能会看到错误位置的某些顶点. 我认为这与指标有关，但我不确定. 我注意到这取决于我使用的堆栈或切片的数量
It seems to work but I have some issue. Looking the image it is possible to see some vertex in the wrong position. I think that is something related to the indicies but I'm not sure. I have notice that depends by the number of stacks or slices that I use
更新:
UPDATE:
我考虑了@ Rabbid76的建议，这就是结果. 渲染中不再有退化的顶点和三角形. 但是渲染不等于@ Rabbid76的渲染，就像顶点旋转一样.
I take into account the suggestion of @Rabbid76 and this is the result. No more degenerated vertex and triangles in the rendering. However the rendering is not equal to the one of @Rabbid76 there is like a rotation of the vertex.
最终:
FINAL:
这是创建顶点和索引的代码:
This is the creation vertex and indices code:
std::vector<glm::vec3> positions;
std::vector<glm::vec3> normals;
std::vector<glm::vec2> textureCoords;
for(int i = 0; i <= stacks; ++i) {
// V texture coordinate.
float V = i / (float)stacks;
float phi = V * M_PI;
for( int j = 0; j <= slices; ++j) {
// U texture coordinate.
float U = j / (float)slices;
float theta = U * 2.0f * M_PI;
float X = cos(theta) * sin(phi);
float Y = cos(phi);
float Z = sin(theta) * sin(phi);
positions.push_back( glm::vec3( X, Y, Z) * radius );
normals.push_back( glm::vec3(X, Y, Z) );
textureCoords.push_back( glm::vec2(U, V) );
}
}
// Now generate the index buffer
std::vector<GLuint> indicies;
int noPerSlice = slices + 1;
for(int i=0; i < stacks; ++i) {
for (int j=0; j < slices; ++j) {
int start_i = (i * noPerSlice) + j;
indicies.push_back( start_i );
indicies.push_back( start_i + noPerSlice + 1 );
indicies.push_back( start_i + noPerSlice );
indicies.push_back( start_i + noPerSlice + 1 );
indicies.push_back( start_i );
indicies.push_back( start_i + 1 );
}
}
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
glGenBuffers(4, vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo[0]);
glBufferData(GL_ARRAY_BUFFER, positions.size() * sizeof(glm::vec3), positions.data(), GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, nullptr);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, vbo[1]);
glBufferData(GL_ARRAY_BUFFER, normals.size() * sizeof(glm::vec3), normals.data(), GL_STATIC_DRAW);
glVertexAttribPointer(2, 3, GL_FLOAT, GL_TRUE, 0, nullptr);
glEnableVertexAttribArray(2);
glBindBuffer(GL_ARRAY_BUFFER, vbo[2]);
glBufferData(GL_ARRAY_BUFFER, textureCoords.size() * sizeof(glm::vec2), textureCoords.data(), GL_STATIC_DRAW);
glVertexAttribPointer(8, 2, GL_FLOAT, GL_FALSE, 0, nullptr);
glEnableVertexAttribArray(8);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vbo[3]);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, indicies.size() * sizeof(GLuint), indicies.data(), GL_STATIC_DRAW);
glBindVertexArray(0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
这是渲染图:
glBindVertexArray(vao);
glEnableVertexAttribArray(0);
if(style == glObject::STYLE::WIREFRAME) glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
if(style == glObject::STYLE::SOLID) glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
glDrawElements(GL_TRIANGLES, (slices * stacks + slices) * 6, GL_UNSIGNED_INT, nullptr);
glBindVertexArray(0);
推荐答案
您已经混淆了phi和theta. theta是围绕切片圆周的点的角度，范围为[0，2 * PI]. phi是点在[-PI，PI]范围内从南到北的角度:
You have confused phi and theta. theta is the angle of the points around the circumference of a slice in range [0, 2*PI]. phi is the angle of the points form the south to the north in range [-PI, PI]:
for (int i = 0; i <= stacks; ++i) {
// V texture coordinate
float V = i / (float)stacks;
float phi = V * M_PI - M_PI/2.0;
for ( int j = 0; j <= slices; ++j) {
// U texture coordinate
float U = j / (float)slices;
float theta = U * _2pi;
float X = a * cos(phi) * cos(theta);
float Y = b * cos(phi) * sin(theta);
float Z = c * sin(phi);
positions.push_back( glm::vec3( X, Y, Z) );
normals.push_back( glm::vec3(X, Y, Z) );
textureCoords.push_back( glm::vec2(U, V) );
}
}
一个切片(围绕圆周)的点数为noPerSlice = slices + 1.四边形的一个点的第一个索引是start_i = (i * noPerSlice) + j，其中i是堆栈的索引，而j是切片周围的索引.围绕圆周创建slices方形，并且stacks切片从南到北形成:
The number of points of a slice (around the circumference) is noPerSlice = slices + 1. The first index of a point of a quad is start_i = (i * noPerSlice) + j, where i is the index of the stack and j the index around the slice. Create slices quads around the circumference and stacks slices form the south to the north:
int noPerSlice = slices + 1;
for(int i=0; i < stacks; ++i) {
for (int j = 0; j < slices; ++j) {
int start_i = (i * noPerSlice) + j;
indicies.push_back( start_i );
indicies.push_back( start_i + noPerSlice + 1 );
indicies.push_back( start_i + noPerSlice );
indicies.push_back( start_i + noPerSlice + 1 );
indicies.push_back( start_i );
indicies.push_back( start_i + 1 );
}
}
这篇关于用OpenGL绘制椭球时的问题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！
