您好,我正在编写一个3D建模应用程序,并希望在OpenGL中加速渲染。目前我使用的是glBegin / glEnd,这是一种非常慢且已经过时的方法。我需要绘制非常快速的平面阴影模型。我每个帧都在CPU上生成法向量,这非常慢。我尝试使用具有索引几何的glDrawElements,但是在法线生成方面有问题,因为法线是在顶点而不是三角形级别指定的。
另一个想法是使用GLSL在几何着色器中在GPU上生成法线。 我为法线生成编写了以下代码:
#version 120
#extension GL_EXT_geometry_shader4 : enable
vec3 NormalFromTriangleVertices(vec3 triangleVertices[3])
{
// now is same as RedBook (OpenGL Programming Guide)
vec3 u = triangleVertices[0] - triangleVertices[1];
vec3 v = triangleVertices[1] - triangleVertices[2];
return cross(v, u);
}
void main()
{
// no change of position
// computes normal from input triangle and front color for that triangle
vec3 triangleVertices[3];
vec3 computedNormal;
vec3 normal, lightDir;
vec4 diffuse;
float NdotL;
vec4 finalColor;
for(int i = 0; i < gl_VerticesIn; i += 3)
{
for (int j = 0; j < 3; j++)
{
triangleVertices[j] = gl_PositionIn[i + j].xyz;
}
computedNormal = NormalFromTriangleVertices(triangleVertices);
normal = normalize(gl_NormalMatrix * computedNormal);
// hardcoded light direction
vec4 light = gl_ModelViewMatrix * vec4(0.0, 0.0, 1.0, 0.0);
lightDir = normalize(light.xyz);
NdotL = max(dot(normal, lightDir), 0.0);
// hardcoded
diffuse = vec4(0.5, 0.5, 0.9, 1.0);
finalColor = NdotL * diffuse;
finalColor.a = 1.0; // final color ignores everything, except lighting
for (int j = 0; j < 3; j++)
{
gl_FrontColor = finalColor;
gl_Position = gl_PositionIn[i + j];
EmitVertex();
}
}
EndPrimitive();
}
当我将着色器集成到我的应用程序中时,没有速度提升发生。它比以前还要糟糕。我是GLSL和着色器总体上的新手,所以我不知道我做错了什么。 我在带有Geforce 9400M的MacBook上尝试了这段代码。 更明确地说,这是我想要替换的代码:
- (void)drawAsCommandsWithScale:(Vector3D)scale
{
float frontDiffuse[4] = { 0.4, 0.4, 0.4, 1 };
CGFloat components[4];
[color getComponents:components];
float backDiffuse[4];
float selectedDiffuse[4] = { 1.0f, 0.0f, 0.0f, 1 };
for (uint i = 0; i < 4; i++)
backDiffuse[i] = components[i];
glMaterialfv(GL_BACK, GL_DIFFUSE, backDiffuse);
glMaterialfv(GL_FRONT, GL_DIFFUSE, frontDiffuse);
Vector3D triangleVertices[3];
float *lastDiffuse = frontDiffuse;
BOOL flip = scale.x < 0.0f || scale.y < 0.0f || scale.z < 0.0f;
glBegin(GL_TRIANGLES);
for (uint i = 0; i < triangles->size(); i++)
{
if (selectionMode == MeshSelectionModeTriangles)
{
if (selected->at(i))
{
if (lastDiffuse == frontDiffuse)
{
glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, selectedDiffuse);
lastDiffuse = selectedDiffuse;
}
}
else if (lastDiffuse == selectedDiffuse)
{
glMaterialfv(GL_BACK, GL_DIFFUSE, backDiffuse);
glMaterialfv(GL_FRONT, GL_DIFFUSE, frontDiffuse);
lastDiffuse = frontDiffuse;
}
}
Triangle currentTriangle = [self triangleAtIndex:i];
if (flip)
currentTriangle = FlipTriangle(currentTriangle);
[self getTriangleVertices:triangleVertices fromTriangle:currentTriangle];
for (uint j = 0; j < 3; j++)
{
for (uint k = 0; k < 3; k++)
{
triangleVertices[j][k] *= scale[k];
}
}
Vector3D n = NormalFromTriangleVertices(triangleVertices);
n.Normalize();
for (uint j = 0; j < 3; j++)
{
glNormal3f(n.x, n.y, n.z);
glVertex3f(triangleVertices[j].x, triangleVertices[j].y, triangleVertices[j].z);
}
}
glEnd();
}
正如你所看到的,这非常低效,但它可以工作。triangles
是一个指向vertices
数组中索引的数组。
我尝试使用这段代码进行绘制,但我不能只有一个索引数组而不是两个(一个用于顶点,另一个用于法线)。
glEnableClientState(GL_VERTEX_ARRAY);
uint *trianglePtr = (uint *)(&(*triangles)[0]);
float *vertexPtr = (float *)(&(*vertices)[0]);
glVertexPointer(3, GL_FLOAT, 0, vertexPtr);
glDrawElements(GL_TRIANGLES, triangles->size() * 3, GL_UNSIGNED_INT, trianglePtr);
glDisableClientState(GL_VERTEX_ARRAY);
现在,当一些顶点被不同的三角形共享时,我该如何指定法线指针,以便为它们提供不同的法线?