[英]OpenGL ES 2.0 (specifically for the iphone) rendering is slightly off. Best guess is it's a projection matrix problem
因此,我购买了O'reilly的Iphone 3D编程,发现我认为那是代码中的错误。 但是我无法弄清楚问题出在哪里,除非我不这样做,否则我将无法继续开发自己的代码。
我会将我认为合适的代码粘贴到这篇文章中,但是幸运的是,所有代码都可以在线获得: http : //examples.oreilly.com/9780596804831/HelloCone/
我遇到的问题是他们的OpenGL ES 2.0渲染器,它没有出现在他们的ES 1.1渲染器中。
因此,我一直在注意的是,圆锥体无法准确地渲染到正确的位置。 为了测试这一点,我更改了ModelViewMatrix以使其完全在FrustumNear平面上呈现。 因此,圆锥体应完全切成两半。 当我使用ES 1.1渲染器执行此操作时,就是这种情况,当我在OpenGL ES 2.0中执行相同操作时却并非如此。 圆锥大部分位于那儿,但稍微削掉了。 这意味着它没有完全落在平顶头的近脸上。
这是创建和设置投影矩阵的初始化代码:
void RenderingEngine2::Initialize(int width, int height)
{
const float coneRadius = 0.5f;
const float coneHeight = 1.0f;
const int coneSlices = 40;
{
// Allocate space for the cone vertices.
m_cone.resize((coneSlices + 1) * 2);
// Initialize the vertices of the triangle strip.
vector<Vertex>::iterator vertex = m_cone.begin();
const float dtheta = TwoPi / coneSlices;
for (float theta = 0; vertex != m_cone.end(); theta += dtheta) {
// Grayscale gradient
float brightness = abs(sin(theta));
vec4 color(brightness, brightness, brightness, 1);
// Apex vertex
vertex->Position = vec3(0, 1, 0);
vertex->Color = color;
vertex++;
// Rim vertex
vertex->Position.x = coneRadius * cos(theta);
vertex->Position.y = 1 - coneHeight;
vertex->Position.z = coneRadius * sin(theta);
vertex->Color = color;
vertex++;
}
}
{
// Allocate space for the disk vertices.
m_disk.resize(coneSlices + 2);
// Initialize the center vertex of the triangle fan.
vector<Vertex>::iterator vertex = m_disk.begin();
vertex->Color = vec4(0.75, 0.75, 0.75, 1);
vertex->Position.x = 0;
vertex->Position.y = 1 - coneHeight;
vertex->Position.z = 0;
vertex++;
// Initialize the rim vertices of the triangle fan.
const float dtheta = TwoPi / coneSlices;
for (float theta = 0; vertex != m_disk.end(); theta += dtheta) {
vertex->Color = vec4(0.75, 0.75, 0.75, 1);
vertex->Position.x = coneRadius * cos(theta);
vertex->Position.y = 1 - coneHeight;
vertex->Position.z = coneRadius * sin(theta);
vertex++;
}
}
// Create the depth buffer.
glGenRenderbuffers(1, &m_depthRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, m_depthRenderbuffer);
glRenderbufferStorage(GL_RENDERBUFFER,
GL_DEPTH_COMPONENT16,
width,
height);
// Create the framebuffer object; attach the depth and color buffers.
glGenFramebuffers(1, &m_framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, m_framebuffer);
glFramebufferRenderbuffer(GL_FRAMEBUFFER,
GL_COLOR_ATTACHMENT0,
GL_RENDERBUFFER,
m_colorRenderbuffer);
glFramebufferRenderbuffer(GL_FRAMEBUFFER,
GL_DEPTH_ATTACHMENT,
GL_RENDERBUFFER,
m_depthRenderbuffer);
// Bind the color buffer for rendering.
glBindRenderbuffer(GL_RENDERBUFFER, m_colorRenderbuffer);
// Set up some GL state.
glViewport(0, 0, width, height);
glEnable(GL_DEPTH_TEST);
// Build the GLSL program.
m_simpleProgram = BuildProgram(SimpleVertexShader, SimpleFragmentShader);
glUseProgram(m_simpleProgram);
// Set the projection matrix.
GLint projectionUniform = glGetUniformLocation(m_simpleProgram, "Projection");
mat4 projectionMatrix = mat4::Frustum(-1.6f, 1.6, -2.4, 2.4, 5, 10);
glUniformMatrix4fv(projectionUniform, 1, 0, projectionMatrix.Pointer());
}
这是渲染代码。 如您所见,我已经更改了ModelVieMatrix,以将圆锥体放置在靠近Frustum面的左下角。
void RenderingEngine2::Render() const
{
GLuint positionSlot = glGetAttribLocation(m_simpleProgram, "Position");
GLuint colorSlot = glGetAttribLocation(m_simpleProgram, "SourceColor");
glClearColor(0.5f, 0.5f, 0.5f, 1);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnableVertexAttribArray(positionSlot);
glEnableVertexAttribArray(colorSlot);
mat4旋转(m_animation.Current.ToMatrix()); mat4翻译= mat4 :: Translate(-1.6,-2.4,-5);
// Set the model-view matrix.
GLint modelviewUniform = glGetUniformLocation(m_simpleProgram, "Modelview");
mat4 modelviewMatrix = rotation * translation;
glUniformMatrix4fv(modelviewUniform, 1, 0, modelviewMatrix.Pointer());
// Draw the cone.
{
GLsizei stride = sizeof(Vertex);
const GLvoid* pCoords = &m_cone[0].Position.x;
const GLvoid* pColors = &m_cone[0].Color.x;
glVertexAttribPointer(positionSlot, 3, GL_FLOAT, GL_FALSE, stride, pCoords);
glVertexAttribPointer(colorSlot, 4, GL_FLOAT, GL_FALSE, stride, pColors);
glDrawArrays(GL_TRIANGLE_STRIP, 0, m_cone.size());
}
// Draw the disk that caps off the base of the cone.
{
GLsizei stride = sizeof(Vertex);
const GLvoid* pCoords = &m_disk[0].Position.x;
const GLvoid* pColors = &m_disk[0].Color.x;
glVertexAttribPointer(positionSlot, 3, GL_FLOAT, GL_FALSE, stride, pCoords);
glVertexAttribPointer(colorSlot, 4, GL_FLOAT, GL_FALSE, stride, pColors);
glDrawArrays(GL_TRIANGLE_FAN, 0, m_disk.size());
}
glDisableVertexAttribArray(positionSlot);
glDisableVertexAttribArray(colorSlot);
}
看起来我找到了自己问题的答案。
O'Reilly代码中的投影矩阵计算不正确。
在他们的代码中,他们有:
T a = 2 * near / (right - left);
T b = 2 * near / (top - bottom);
T c = (right + left) / (right - left);
T d = (top + bottom) / (top - bottom);
T e = - (far + near) / (far - near);
T f = -2 * far * near / (far - near);
Matrix4 m;
m.x.x = a; m.x.y = 0; m.x.z = 0; m.x.w = 0;
m.y.x = 0; m.y.y = b; m.y.z = 0; m.y.w = 0;
m.z.x = c; m.z.y = d; m.z.z = e; m.z.w = -1;
m.w.x = 0; m.w.y = 0; m.w.z = f; m.w.w = 1;
return m;
但是,这不是投影矩阵。 mww应该为0而不是1。
Matrix4 m;
m.x.x = a; m.x.y = 0; m.x.z = 0; m.x.w = 0;
m.y.x = 0; m.y.y = b; m.y.z = 0; m.y.w = 0;
m.z.x = c; m.z.y = d; m.z.z = e; m.z.w = -1;
m.w.x = 0; m.w.y = 0; m.w.z = f; m.w.w = 0;
return m;
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.