我用c++写了一个最小的代码示例，它渲染10000种颜色屏幕上有四边形。我使用"实例化"，所以只更新每一帧的模型矩阵。6个顶点的数据存储在单独的VBO中，并且将一直被重用。投影矩阵(正字法)在程序启动时被注入通过统一的。模型矩阵在CPU上使用库GLM进行计算。我测量了渲染时间，我得到的平均FPS只有52。我认为这是多到少，但我找不到错误/瓶颈在我的小样本程序。
经过分析，这3个计算似乎是用GLM完成的都很慢。我做错什么了吗?例如，如果移除旋转计算后，我的FPS提升了10帧!也许你可以帮我找出，我在这里可以做得更好的地方，以及如何做我可以优化我的样本。对我来说很重要的是，每个四元组在运行时都是单独可配置的，所以我决定使用实例化。将矩阵计算移动到GPU似乎是另一种选择，但我真的很困惑，为什么CPU在计算10000时有这么多问题model-matrices !好吧，我的CPU非常糟糕(Athlon 2 Core-Duo M300, GPU是ATI Mobility Radeon 4100)，但它应该在没有可测量的时间内完成这个任务，或者?
这是一个最小的，完全工作的，可编译的例子(如果你有GLFW和GLM)。也许有人有时间可以帮我一下:)
#define GLEW_STATIC
#define GLM_FORCE_INLINE
#define GLM_FORCE_SSE2
#include "glew.h"
#include "glfw3.h"
#include "glm.hpp"
#include "glm/gtc/matrix_transform.hpp"
#include <conio.h>
#include <cstdlib>
#include <iostream>
#include <ctime>
GLuint buildShader()
{
std::string strVSCode =
"#version 330 coren"
"in vec3 vertexPosition;n"
"in mat4 modelMatrix;n"
"uniform mat4 projectionMatrix;n"
"out vec4 m_color;n"
"void main() {n"
" vec4 vecVertex = vec4(vertexPosition, 1);n"
" gl_Position = projectionMatrix * modelMatrix * vecVertex;n"
" m_color = gl_Position;n"
"}n";
std::string strFSCode = "#version 330 coren"
"out vec4 frag_colour;n"
"in vec4 m_color;n"
"void main() {n"
" frag_colour = vec4(m_color.x, m_color.y, m_color.z, 0.5f);n"
"}n";
GLuint gluiVertexShaderId = glCreateShader(GL_VERTEX_SHADER);
char const * VertexSourcePointer = strVSCode.c_str();
glShaderSource(gluiVertexShaderId, 1, &VertexSourcePointer, NULL);
glCompileShader(gluiVertexShaderId);
GLuint gluiFragmentShaderId = glCreateShader(GL_FRAGMENT_SHADER);
char const * FragmentSourcePointer = strFSCode.c_str();
glShaderSource(gluiFragmentShaderId, 1, &FragmentSourcePointer, NULL);
glCompileShader(gluiFragmentShaderId);
GLuint gluiProgramId = glCreateProgram();
glAttachShader(gluiProgramId, gluiVertexShaderId);
glAttachShader(gluiProgramId, gluiFragmentShaderId);
glLinkProgram(gluiProgramId);
glDeleteShader(gluiVertexShaderId);
glDeleteShader(gluiFragmentShaderId);
return gluiProgramId;
}
struct Sprite
{
glm::vec3 position, dimension;
float speed, rotation, rx, ry;
};
struct Vertex
{
float x, y, z;
Vertex(){};
Vertex(float x, float y, float z) : x(x), y(y), z(z) {}
};
int main(int arc, char **argv)
{
// GLFW init
int displayResWith = 1366; //modify this here
int displayResHeight = 768; //modify this here
glfwInit();
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, 1);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
glfwWindowHint(GLFW_RED_BITS, 8);
glfwWindowHint(GLFW_GREEN_BITS, 8);
glfwWindowHint(GLFW_BLUE_BITS, 8);
glfwWindowHint(GLFW_ALPHA_BITS, 8);
glfwWindowHint(GLFW_DEPTH_BITS, 32);
glfwWindowHint(GLFW_STENCIL_BITS, 32);
GLFWwindow* window = glfwCreateWindow(displayResWith, displayResHeight,"Instancing", glfwGetPrimaryMonitor(),NULL);
int width, height;
glfwMakeContextCurrent(window);
glfwSwapInterval(0);
glfwGetFramebufferSize(window, &width, &height);
//GLEW init
glewExperimental = GL_TRUE;
glewInit();
const GLubyte* renderer = glGetString(GL_RENDERER);
const GLubyte* version = glGetString(GL_VERSION);
std::cout << "Renderer: " << renderer << std::endl;
std::cout << "OpenGL supported version: " << version << std::endl;
//OpenGL init
glEnable(GL_CULL_FACE);
glCullFace(GL_BACK);
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LESS);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glClearColor(255.0f, 255.0f, 255.0f, 255.0f);
//Shader
GLuint programID = buildShader();
//VBO vertexBuffer
GLuint vertexBuffer;
glGenBuffers(1, &vertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
Vertex VertexBufferData[6];
VertexBufferData[0] = Vertex(-0.5f, 0.5f, 0.0f); //Links oben
VertexBufferData[1] = Vertex(-0.5f, -0.5f, 0.0f); //Links unten
VertexBufferData[2] = Vertex(0.5f, -0.5f, 0.0f); //Rechts unten
VertexBufferData[3] = VertexBufferData[2]; //Rechts unten
VertexBufferData[4] = Vertex(0.5f, 0.5f, 0.0f); //Rechts oben
VertexBufferData[5] = VertexBufferData[0]; //Links oben
glBufferData(GL_ARRAY_BUFFER, sizeof(Vertex)*6, VertexBufferData, GL_STATIC_DRAW);
//VBO instanceBuffer
GLuint instanceBuffer;
glGenBuffers(1, &instanceBuffer);
glBindBuffer(GL_ARRAY_BUFFER, instanceBuffer);
int iMaxInstanceCount = 30000;
glm::mat4 *ptrInstanceBufferData = new glm::mat4[iMaxInstanceCount];
glBufferData(GL_ARRAY_BUFFER, iMaxInstanceCount * sizeof(glm::mat4), NULL, GL_STREAM_DRAW);
//VAO - Start
GLuint vertexArrayObject;
glGenVertexArrays(1, &vertexArrayObject);
glBindVertexArray(vertexArrayObject);
//For VBO vertexbuffer
glEnableVertexAttribArray(glGetAttribLocation(programID, "vertexPosition"));
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
glVertexAttribPointer(
glGetAttribLocation(programID, "vertexPosition"),
3,
GL_FLOAT,
GL_FALSE,
sizeof(Vertex),
(void*)0
);
glVertexAttribDivisor(0, 0);
//For VBO instanceBuffer
int pos = glGetAttribLocation(programID, "modelMatrix");
int pos1 = pos + 0;
int pos2 = pos + 1;
int pos3 = pos + 2;
int pos4 = pos + 3;
glEnableVertexAttribArray(pos1);
glEnableVertexAttribArray(pos2);
glEnableVertexAttribArray(pos3);
glEnableVertexAttribArray(pos4);
glBindBuffer(GL_ARRAY_BUFFER, instanceBuffer);
glVertexAttribPointer(pos1, 4, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4 * 4, (void*)(0));
glVertexAttribPointer(pos2, 4, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4 * 4, (void*)(sizeof(float) * 4));
glVertexAttribPointer(pos3, 4, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4 * 4, (void*)(sizeof(float) * 8));
glVertexAttribPointer(pos4, 4, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4 * 4, (void*)(sizeof(float) * 12));
glVertexAttribDivisor(pos1, 1);
glVertexAttribDivisor(pos2, 1);
glVertexAttribDivisor(pos3, 1);
glVertexAttribDivisor(pos4, 1);
glBindVertexArray(0); //VAO - End
//Matrix vars
glm::mat4 Projection, Rotating, Scaling, Translation, Identity;
glm::vec3 ZRotateVec(0.0f, 0.0f, 1.0f);
//Calc projection-matrix and put shader (uniform)
Projection = glm::ortho(0.0f, (float)width, 0.0f, (float)height, 0.0f, 1.0f);
glUseProgram(programID);
glUniformMatrix4fv(glGetUniformLocation(programID, "projectionMatrix"), 1, GL_FALSE, &Projection[0][0]);
//Creating sprites
std::srand(static_cast<unsigned int>(std::time(0)));
int iActInstanceCount = 10000;
Sprite *ptrSprites = new Sprite[iActInstanceCount];
for (int i = 0; i < iActInstanceCount; ++i)
{
ptrSprites[i].dimension = glm::vec3(16, 16, 1.0f);
ptrSprites[i].position = glm::vec3(std::rand()%(width-32),std::rand()%(height-32),-1.0f *((std::rand()%256)/256.0f));
ptrSprites[i].rotation = rand() % 360 + 0.0f;
ptrSprites[i].rx = static_cast<float>(std::rand() % 2);
ptrSprites[i].ry = static_cast<float>(std::rand() % 2);
ptrSprites[i].speed = (std::rand() % 100) + 1.0f;
if (ptrSprites[i].speed < 1.0f) ptrSprites[i].speed = 1.0f;
}
//FPS init
double fFramesRendered = 0.0f;
double fFrameMeasurementStart = 0.0f;
double fFPS = 0.0f;
double fCurrentTime = 0.0f;
glfwSetTime(0);
//Main-loop (also renderloop)
while (!glfwWindowShouldClose(window))
{
//application-logic
if (glfwGetKey(window, GLFW_KEY_ESCAPE)== GLFW_PRESS)
glfwSetWindowShouldClose(window, GL_TRUE);
const double fNewTime = glfwGetTime();
double fDeltaTime = fNewTime - fCurrentTime;
fCurrentTime = fNewTime;
for (int i = 0; i < iActInstanceCount; ++i)
{
float fSpeed = ptrSprites[i].speed * static_cast<float>(fDeltaTime);
ptrSprites[i].rotation += fSpeed;
if (ptrSprites[i].rotation >= 360.0f) ptrSprites[i].rotation = 0.0f;
if (ptrSprites[i].rx == 1) ptrSprites[i].position.x = ptrSprites[i].position.x + fSpeed;
if (ptrSprites[i].rx == 0) ptrSprites[i].position.x = ptrSprites[i].position.x - fSpeed;
if (ptrSprites[i].ry == 1) ptrSprites[i].position.y = ptrSprites[i].position.y + fSpeed;
if (ptrSprites[i].ry == 0) ptrSprites[i].position.y = ptrSprites[i].position.y - fSpeed;
if (ptrSprites[i].position.x <= 0) ptrSprites[i].rx = 1;
if (ptrSprites[i].position.x + ptrSprites[i].dimension.x >= width) ptrSprites[i].rx = 0;
if (ptrSprites[i].position.y <= 0) ptrSprites[i].ry = 1;
if (ptrSprites[i].position.y + ptrSprites[i].dimension.y >= height) ptrSprites[i].ry = 0;
//matrix-calculations (saved in local buffer)
Translation = glm::translate(Identity, ptrSprites[i].position + glm::vec3(ptrSprites[i].dimension.x / 2.0f, ptrSprites[i].dimension.y / 2.0f, 0.0f));
Scaling = glm::scale(Translation, ptrSprites[i].dimension);
ptrInstanceBufferData[i] = glm::rotate(Scaling, ptrSprites[i].rotation, ZRotateVec);
}
//render-call
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glUseProgram(programID);
glBindVertexArray(vertexArrayObject);
glBindBuffer(GL_ARRAY_BUFFER, instanceBuffer);
glBufferData(GL_ARRAY_BUFFER, iMaxInstanceCount * sizeof(glm::mat4), NULL, GL_STREAM_DRAW); // Buffer orphaning
glBufferSubData(GL_ARRAY_BUFFER, 0, iActInstanceCount * sizeof(glm::mat4), ptrInstanceBufferData);
glDrawArraysInstanced(GL_TRIANGLES, 0, 6, iActInstanceCount);
glBindVertexArray(0);
glfwSwapBuffers(window);
glfwPollEvents();
//FPS-stuff
++fFramesRendered;
if ((fCurrentTime*1000.0f) >= (fFrameMeasurementStart*1000.0f) + 1000.0f)
{
fFPS = ((fCurrentTime*1000.0f) - (fFrameMeasurementStart*1000.0f)) / 1000.0f * fFramesRendered;
fFrameMeasurementStart = fCurrentTime;
fFramesRendered = 0;
std::cout << "FPS: " << fFPS << std::endl;
}
}
//Termination and cleanup
glDeleteBuffers(1, &vertexBuffer);
glDeleteBuffers(1, &instanceBuffer);
glDeleteVertexArrays(1, &vertexArrayObject);
glDeleteProgram(programID);
glfwDestroyWindow(window);
glfwTerminate();
return _getch();
}
嗯，在我的机器上测试之后，它肯定是CPU有限的，所以您对OGL所做的任何事情都不会产生太大的影响。在GCC至少为- 0的情况下，我得到了大约300fps，但在- 0的情况下只有~80 fps。我的CPU非常快(i7 2600k, 4.7ghz)，但我的GPU相当慢(GT 520)。我也在Ubuntu上。
一些快速的想法，可能会加快一点:
- 将顶点位置放在顶点着色器的数组中，并使用gl_VertexID来访问它们
- 使用GL_TRIANGLE_STRIP代替gl_triangle
- 使用弧度表示角度，否则GLM必须转换它们
这些都不太可能产生任何影响，真的。只要确保编译器设置正确，可能就没有太多要做的了。