Ho riscontrato un problema di prestazioni piuttosto strano. Finora ho ridotto il problema a questo: sto rendendo i cubi 20x20x20 in una griglia, usando glDrawElementsInstanced
, che funziona bene finché la mia macchina fotografica è lontana dall'origine, tuttavia quando si avvicina all'origine, inizia fermandosi.Curioso rallentamento in opengl quando si utilizza il rendering istanza
sto definendo il mio modello matrice di proiezione vista attraverso:
float distance=3.8;
Projection = glm::perspective(65.0f, (float)(width)/height, 0.1f, 300.0f);
View = glm::lookAt( glm::vec3(0,0,-distance),
glm::vec3(0,0,10),
glm::vec3(0,1,0));
Model = glm::rotate(glm::mat4(1.0f), 0.0f, glm::vec3(0.25f, 1.0f,0.75f));
Con la distanza a 40, non ci sono problemi, ma quando la distanza si riduce a circa 3,8 e inferiore, tutto si blocca.
La chiamata effettiva al rendering viene effettuato attraverso:
glBindVertexArray(cubeVAO);
glDrawElementsInstanced(GL_TRIANGLES, indices.size(),GL_UNSIGNED_INT,(GLvoid*)(0),latticePoints.size());
Mentre mettendo tutti i vertici in un unico buffer e il rendering chiamando:
glBindVertexArray(nonInstancedVAO);
glDrawArrays(GL_TRIANGLES, 0,vertices.size());
rimuove completamente il comportamento. Chiunque abbia avuto un comportamento simile che possa indicarmi la direzione di una soluzione? In caso contrario, chiunque abbia un'idea di come rintracciare qualcosa di simile? Speravo di poter determinare cosa stava causando il rallentamento con gDEBugger, ma questo semplicemente riconferma che non ci sono altre chiamate opengl, e in realtà non aiuta a capire cosa sta occupando tutto il tempo di elaborazione.
Un'altra nota è che glDrawArraysInstanced mostra anche lo stesso rallentamento e che suddividendo la chiamata in 4 chiamate separate con un quarto della geometria cessa anche il rallentamento.
Aggiornamento
Ecco un tentativo di illustrazione minima del problema.
//Minimal reproduction of problem
#include <stdio.h>
#include <string>
#include <fstream>
#include <stdlib.h>
#include <string.h>
#include <GL/glew.h>
#include <GLFW/glfw3.h>
// Include GLM
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>
#include <vector>
#include <iostream>
#include <stdio.h>
//Set to true to use instanced rendering (glDrawElementsInstanced), false to render a generated grid instead (glDrawElements)
#define Instanced true
//Translation from origin. Problme is pressent at 0 distance, but disapears at ex. 40.
const float distanceFromOrigin=0;
// Function to load shaders
GLuint LoadShaders(const char * vertex_file_path,const char * fragment_file_path);
int main(){
int width, height;
bool running = true;
// Initialise GLFW
glfwInit();
glfwWindowHint(GLFW_SAMPLES,1);
glfwWindowHint(GLFW_OPENGL_DEBUG_CONTEXT,GL_TRUE);
glfwWindowHint(GLFW_VERSION_MAJOR, 4);
GLFWwindow* windowRef = glfwCreateWindow(512, 512, "",0,0);
glfwMakeContextCurrent(windowRef);
glewInit();
//Load Shader
GLuint programID = LoadShaders("Simple.vs.c", "Simple.fs.c");
GLuint MatrixID = glGetUniformLocation(programID, "MVP");
glUseProgram(programID);
glm::mat4 Model,Projection,MVP,View,checkMVP;
std::vector<GLuint> sqIndice = {3,2,1,1,0,3,4,5,6,6,7,4,0,4,7,7,3,0,0,1,5,5,4,0,2,3,7,7,6,2,6,5,1,1,2,6,0,4,7,7,3,0};
std::vector<GLfloat> sqVertex = {-1, 1, -1, -1, 1, 1, -1, -1, 1, -1, -1, -1, 1, 1, -1, 1, 1, 1, 1, -1, 1, 1, -1, -1};
std::vector<GLfloat> sqColor = {0.2472,0.24,0.6,0.6,0.24,0.442893,0.6,0.547014,0.24,0.24,0.6,0.33692,0.24,0.353173,0.6,0.6,0.24,0.563266,0.6,0.426641,0.24,0.263452,0.6,0.24};
const float lattice = 5;
const int mxn = 10;
std::vector<GLfloat> v1 = {lattice,-1,0};
std::vector<GLfloat> v2 = {1,lattice,0};
std::vector<GLfloat> v3 = {0,0,lattice};
std::vector<GLfloat> offset = {0,0,-distanceFromOrigin};
std::vector<GLfloat> latticePoints,sqVertexGrid,sqColorGrid;// = {0,0,0};
std::vector<GLuint> sqIndiceGrid;
// Looping stuff to generate the full grid of "instances" to render in a single call.
int instanceCount=0;
//Generate Lattice vectors, aswell as a vector containing the full grids of indices,vertexes and colors
for(int x=-mxn;x<mxn;++x){
for(int y=-mxn;y<mxn;++y){
for(int z=-mxn;z<mxn;++z){
for(int n=0;n<3;++n){
latticePoints.push_back(x*v1[n]+y*v2[n]+z*v3[n]+offset[n]);
};
for(int elm=0;elm<sqVertex.size();elm+=3){
for(int n=0;n<3;++n){
sqVertexGrid.push_back(sqVertex[elm+n]+x*v1[n]+y*v2[n]+z*v3[n]+offset[n]);
sqColorGrid.push_back(sqColor[elm+n]);
};
};
for(int elm=0;elm<sqIndice.size();++elm){
sqIndiceGrid.push_back(sqIndice[elm]+instanceCount*sqVertex.size()/3);
};
++instanceCount;glewInit
};
};
};
#if Instanced==true
//Initialize and fill vertex,color and indice buffers with the relevant data.
GLuint cubeVAO;
glGenVertexArrays(1, &cubeVAO);
glBindVertexArray(cubeVAO);
glEnable(GL_DEPTH_TEST);
//Vertex buffer
GLuint vertexBuffer;
glGenBuffers(1, &vertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
glBufferData(GL_ARRAY_BUFFER, sqVertex.size()*sizeof(GLfloat), &sqVertex[0], GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0,3,GL_FLOAT,GL_FALSE,0,(void*)0);
//Color buffer
GLuint colorBuffer;
glGenBuffers(1, &colorBuffer);
glBindBuffer(GL_ARRAY_BUFFER, colorBuffer);
glBufferData(GL_ARRAY_BUFFER, sqColor.size()*sizeof(GLfloat), &sqColor[0], GL_STATIC_DRAW);
glEnableVertexAttribArray(1);
glVertexAttribPointer(1,3,GL_FLOAT,GL_FALSE,0,(void*)0);
// Indice buffer
GLuint indicesBuffer;
glGenBuffers(1, &indicesBuffer);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indicesBuffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sqIndice.size()*sizeof(GLuint), &sqIndice[0], GL_STATIC_DRAW);
//Lattice point buffer
GLuint latticePointBuffer;
glGenBuffers(1, &latticePointBuffer);
glBindBuffer(GL_ARRAY_BUFFER, latticePointBuffer);
glBufferData(GL_ARRAY_BUFFER, latticePoints.size()*sizeof(GLfloat), &latticePoints[0], GL_STATIC_DRAW);
glEnableVertexAttribArray(2);
glVertexAttribPointer(2,3,GL_FLOAT,GL_FALSE,0,(void*)0);
glVertexAttribDivisor(2,1);
glBindVertexArray(0);
#elif Instanced==false
GLuint cubeGridVAO;
glGenVertexArrays(1, &cubeGridVAO);
glBindVertexArray(cubeGridVAO);
glEnable(GL_DEPTH_TEST);
//Vertex buffer
GLuint vertexBuffer;
glGenBuffers(1, &vertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
glBufferData(GL_ARRAY_BUFFER, sqVertexGrid.size()*sizeof(GLfloat), &sqVertexGrid[0], GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0,3,GL_FLOAT,GL_FALSE,0,(void*)0);
//Color buffer
GLuint colorBuffer;
glGenBuffers(1, &colorBuffer);
glBindBuffer(GL_ARRAY_BUFFER, colorBuffer);
glBufferData(GL_ARRAY_BUFFER, sqColorGrid.size()*sizeof(GLfloat), &sqColorGrid[0], GL_STATIC_DRAW);
glEnableVertexAttribArray(1);
glVertexAttribPointer(1,3,GL_FLOAT,GL_FALSE,0,(void*)0);
// Indice buffer
GLuint indicesBuffer;
glGenBuffers(1, &indicesBuffer);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indicesBuffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sqIndiceGrid.size()*sizeof(GLuint), &sqIndiceGrid[0], GL_STATIC_DRAW);
glBindVertexArray(0);
#endif
while(running)
{
glfwGetFramebufferSize(windowRef, &width, &height);
height = height > 0 ? height : 1;
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
Projection = glm::perspective(65.0f, (float)(width)/height, 0.1f, 300.0f);
View = glm::lookAt( glm::vec3(0.0f,0.0f,-(distanceFromOrigin+3.8f)),
glm::vec3(0.0f,0.0f,100.0f),
glm::vec3(0.0f,1.0f,0.0f));
Model = glm::rotate(glm::mat4(1.0f), 0.0f, glm::vec3(0.25f, 1.0f,0.75f));
MVP = Projection*View*Model;
glUniformMatrix4fv(MatrixID, 1, GL_FALSE, glm::value_ptr(MVP));
#if Instanced==true
glBindVertexArray(cubeVAO);
glDrawElementsInstanced(GL_TRIANGLES, sqIndice.size(),GL_UNSIGNED_INT,(GLvoid*)(0),latticePoints.size());
#elif Instanced==false
glBindVertexArray(cubeGridVAO);
glDrawElements(GL_TRIANGLES, sqIndiceGrid.size(),GL_UNSIGNED_INT,(GLvoid*)(0));
#endif
glfwPollEvents();
glfwSwapBuffers(windowRef);
std::cout<<".\n";
running = !glfwGetKey(windowRef,GLFW_KEY_ESCAPE) && !glfwWindowShouldClose(windowRef);
}
glfwDestroyWindow(windowRef);
glfwTerminate();
return 0;
};
GLuint LoadShaders(const char * vertex_file_path,const char * fragment_file_path){
// Create the shaders
GLuint VertexShaderID = glCreateShader(GL_VERTEX_SHADER);
GLuint FragmentShaderID = glCreateShader(GL_FRAGMENT_SHADER);
// Read the Vertex Shader code from the file
std::string VertexShaderCode;
std::ifstream VertexShaderStream(vertex_file_path, std::ios::in);
if(VertexShaderStream.is_open()){
std::string Line = "";
while(getline(VertexShaderStream, Line))
VertexShaderCode += "\n" + Line;
VertexShaderStream.close();
}else{
printf("Impossible to open %s. Are you in the right directory?\n", vertex_file_path);
return 0;
}
// Read the Fragment Shader code from the file
std::string FragmentShaderCode;
std::ifstream FragmentShaderStream(fragment_file_path, std::ios::in);
if(FragmentShaderStream.is_open()){
std::string Line = "";
while(getline(FragmentShaderStream, Line))
FragmentShaderCode += "\n" + Line;
FragmentShaderStream.close();
}
GLint Result = GL_FALSE;
int InfoLogLength;
// Compile Vertex Shader
printf("Compiling shader : %s\n", vertex_file_path);
char const * VertexSourcePointer = VertexShaderCode.c_str();
glShaderSource(VertexShaderID, 1, &VertexSourcePointer , NULL);
glCompileShader(VertexShaderID);
// Check Vertex Shader
glGetShaderiv(VertexShaderID, GL_COMPILE_STATUS, &Result);
glGetShaderiv(VertexShaderID, GL_INFO_LOG_LENGTH, &InfoLogLength);
if (InfoLogLength > 0){
std::vector<char> VertexShaderErrorMessage(InfoLogLength+1);
glGetShaderInfoLog(VertexShaderID, InfoLogLength, NULL, &VertexShaderErrorMessage[0]);
printf("%s\n", &VertexShaderErrorMessage[0]);
}
// Compile Fragment Shader
printf("Compiling shader : %s\n", fragment_file_path);
char const * FragmentSourcePointer = FragmentShaderCode.c_str();
glShaderSource(FragmentShaderID, 1, &FragmentSourcePointer , NULL);
glCompileShader(FragmentShaderID);
// Check Fragment Shader
glGetShaderiv(FragmentShaderID, GL_COMPILE_STATUS, &Result);
glGetShaderiv(FragmentShaderID, GL_INFO_LOG_LENGTH, &InfoLogLength);
if (InfoLogLength > 0){
std::vector<char> FragmentShaderErrorMessage(InfoLogLength+1);
glGetShaderInfoLog(FragmentShaderID, InfoLogLength, NULL, &FragmentShaderErrorMessage[0]);
printf("%s\n", &FragmentShaderErrorMessage[0]);
}
// Link the program
printf("Linking program\n");
GLuint ProgramID = glCreateProgram();
glAttachShader(ProgramID, VertexShaderID);
glAttachShader(ProgramID, FragmentShaderID);
glLinkProgram(ProgramID);
// Check the program
glGetProgramiv(ProgramID, GL_LINK_STATUS, &Result);
glGetProgramiv(ProgramID, GL_INFO_LOG_LENGTH, &InfoLogLength);
if (InfoLogLength > 0){
std::vector<char> ProgramErrorMessage(InfoLogLength+1);
glGetProgramInfoLog(ProgramID, InfoLogLength, NULL, &ProgramErrorMessage[0]);
printf("%s\n", &ProgramErrorMessage[0]);
}
glDeleteShader(VertexShaderID);
glDeleteShader(FragmentShaderID);
return ProgramID;
}
Non ho una risposta, ma ho letto che l'istanza non è sempre una buona cosa da fare: http://stackoverflow.com/a/11973466/804614. "L'istanza non dovrebbe essere usata con mesh che hanno troppi vertici o troppe poche, 100-1000 circa." Non riesco a spiegarne il motivo, ma se stai rendendo i cubi che sarebbero solo 8 vertici. – Gigo
Grazie per il collegamento, ma la stessa cosa accade con maglie più grandi con 540 vertici. E se il problema era dovuto a questo, non dovrebbe dipendere dalla posizione della telecamera. – jVincent
Ho testato l'istanziamento usando cubi 100^3 (1M) su una 580 GTX a 30-50 fps a seconda della posizione della telecamera. Testato con posizioni casuali e come cubo compatto. Non ho notato alcun rallentamento come descritto qui. Forse il rallentamento è solo causato dalla quantità di superamento, quindi i cubi coprono l'intero schermo e vengono disegnati da dietro in avanti? – Grimmy