我正在努力理解如何适当地使用VAO进行实例渲染(特别是在Qt 5.2中,使用OpenGL 3.3)。我的理解是,VAOs保存VBO和相关属性的状态,因此您无需担心在绘制时绑定和启用所有内容,只需绑定VAO即可。但是对于实例化,您通常有多个VBO。如何避免需要绑定它们全部?或者我只需要使用单个VBO来处理每个顶点数据和每个实例数据?
我一直在查看一些教程,例如:http://ogldev.atspace.co.uk/www/tutorial33/tutorial33.html 在我看来,他所做的是使用VAO来处理每个顶点数据,而不是每个实例数据。我尝试在基于Qt的代码中执行相同的操作,但这对我没有起作用(可能是因为我不完全理解它的工作原理…在绘制发生时,他的实例数据是否仍然需要绑定?)
以下是一些虚拟代码…这有点傻,我只是绘制了两个三角形的单个实例,并使用透视矩阵作为每个实例属性。
看起来我的实例化问题不仅仅是在错误的时间绑定了错误的缓冲区。我还做错了什么?
我一直在查看一些教程,例如:http://ogldev.atspace.co.uk/www/tutorial33/tutorial33.html 在我看来,他所做的是使用VAO来处理每个顶点数据,而不是每个实例数据。我尝试在基于Qt的代码中执行相同的操作,但这对我没有起作用(可能是因为我不完全理解它的工作原理…在绘制发生时,他的实例数据是否仍然需要绑定?)
以下是一些虚拟代码…这有点傻,我只是绘制了两个三角形的单个实例,并使用透视矩阵作为每个实例属性。
glwindow.cpp:
#include "glwindow.h"
#include <QColor>
#include <QMatrix4x4>
#include <QVector>
#include <QVector3D>
#include <QVector4D>
#include <QDebug>
GLWindow::GLWindow(QWindow *parent)
: QWindow(parent)
, _vbo(QOpenGLBuffer::VertexBuffer)
, _matbo(QOpenGLBuffer::VertexBuffer)
, _context(0)
{
setSurfaceType(QWindow::OpenGLSurface);
}
GLWindow::~GLWindow()
{}
void GLWindow::initGL()
{
setupShaders();
_program->bind();
_positionAttr = _program->attributeLocation("position");
_colourAttr = _program->attributeLocation("colour");
_matrixAttr = _program->attributeLocation("matrix");
QVector<QVector3D> triangles;
triangles << QVector3D(-0.5, 0.5, 1) << QVector3D(-0.5, -0.5, 1) << QVector3D(0.5, -0.5, 1);
triangles << QVector3D(0.5, 0.5, 0.5) << QVector3D(-0.5, -0.5, 0.5) << QVector3D(0.5, -0.5, 0.5);
QVector<QVector3D> colours;
colours << QVector3D(1, 0, 0) << QVector3D(0, 1, 0) << QVector3D(0, 0, 1);
colours << QVector3D(1, 1, 1) << QVector3D(1, 1, 1) << QVector3D(1, 1, 1);
_vao.create();
_vao.bind();
_vbo.create();
_vbo.setUsagePattern(QOpenGLBuffer::StaticDraw);
_vbo.bind();
size_t positionSize = triangles.size() * sizeof(QVector3D);
size_t colourSize = colours.size() * sizeof(QVector3D);
_vbo.allocate(positionSize + colourSize);
_vbo.bind();
_vbo.write(0, triangles.constData(), positionSize);
_vbo.write(positionSize, colours.constData(), colourSize);
_colourOffset = positionSize;
_program->setAttributeBuffer(_positionAttr, GL_FLOAT, 0, 3, 0);
_program->setAttributeBuffer(_colourAttr, GL_FLOAT, _colourOffset, 3, 0);
_program->enableAttributeArray(_positionAttr);
_program->enableAttributeArray(_colourAttr);
_vao.release();
_matbo.create();
_matbo.setUsagePattern(QOpenGLBuffer::StaticDraw);
_matbo.bind();
_matbo.allocate(4 * sizeof(QVector4D));
_program->setAttributeBuffer(_matrixAttr, GL_FLOAT, 0, 4, 4 * sizeof(QVector4D));
_program->enableAttributeArray(_matrixAttr);
_func330->glVertexAttribDivisor(_matrixAttr, 1);
_matbo.release();
_program->release();
resizeGL(width(), height());
}
void GLWindow::resizeGL(int w, int h)
{
glViewport(0, 0, w, h);
}
void GLWindow::paintGL()
{
if (! _context) // not yet initialized
return;
_context->makeCurrent(this);
QColor background(Qt::black);
glClearColor(background.redF(), background.greenF(), background.blueF(), 1.0f);
glClearDepth(1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
QMatrix4x4 matrix;
matrix.perspective(60, 4.0/3.0, 0.1, 100.0);
matrix.translate(0, 0, -2);
_program->bind();
_matbo.bind();
_matbo.write(0, matrix.constData(), 4 * sizeof(QVector4D));
_vao.bind();
glEnable(GL_DEPTH_TEST);
_func330->glDrawArraysInstanced(GL_TRIANGLES, 0, 6, 1);
_vao.release();
_program->release();
_context->swapBuffers(this);
_context->doneCurrent();
}
void GLWindow::setupShaders()
{
QString vShaderSrc("#version 330\n"
"layout(location = 0) in vec4 position;\n"
"layout(location = 1) in vec4 colour;\n"
"layout(location = 2) in mat4 matrix;\n"
"smooth out vec4 col;\n"
"void main() {\n"
" col = colour;\n"
" gl_Position = matrix * position;\n"
"}\n");
QString fShaderSrc("#version 330\n"
"smooth in vec4 col;\n"
"void main() {\n"
" gl_FragColor = col;\n"
"}\n");
_program = new QOpenGLShaderProgram(this);
_program->addShaderFromSourceCode(QOpenGLShader::Vertex, vShaderSrc);
_program->addShaderFromSourceCode(QOpenGLShader::Fragment, fShaderSrc);
_program->link();
}
void GLWindow::exposeEvent(QExposeEvent *event)
{
Q_UNUSED(event);
if (isExposed())
{
if (! _context)
{
_context = new QOpenGLContext(this);
QSurfaceFormat format(requestedFormat());
format.setVersion(3,3);
format.setDepthBufferSize(24);
_context->setFormat(format);
_context->create();
_context->makeCurrent(this);
initializeOpenGLFunctions();
_func330 = _context->versionFunctions<QOpenGLFunctions_3_3_Core>();
if (_func330)
_func330->initializeOpenGLFunctions();
else
{
qWarning() << "Could not obtain required OpenGL context version";
exit(1);
}
initGL();
}
paintGL();
}
}
glwindow.h:
#ifndef GL_WINDOW_H
#define GL_WINDOW_H
#include <QExposeEvent>
#include <QSurfaceFormat>
#include <QWindow>
#include <QOpenGLBuffer>
#include <QOpenGLContext>
#include <QOpenGLFunctions>
#include <QOpenGLFunctions_3_3_Core>
#include <QOpenGLShaderProgram>
#include <QOpenGLVertexArrayObject>
class GLWindow : public QWindow, protected QOpenGLFunctions
{
Q_OBJECT
public:
GLWindow(QWindow * = 0);
virtual ~GLWindow();
void initGL();
void paintGL();
void resizeGL(int, int);
protected:
virtual void exposeEvent(QExposeEvent *);
private:
void setupShaders();
QOpenGLBuffer _vbo;
QOpenGLBuffer _matbo;
QOpenGLContext *_context;
QOpenGLShaderProgram *_program;
QOpenGLVertexArrayObject _vao;
QOpenGLFunctions_3_3_Core *_func330;
GLuint _positionAttr;
GLuint _colourAttr;
GLuint _matrixAttr;
size_t _colourOffset;
} ;
#endif
glbuffertest.cpp:
#include <QGuiApplication>
#include <QSurfaceFormat>
#include "glwindow.h"
int main(int argc, char **argv)
{
QGuiApplication app(argc, argv);
GLWindow window;
window.resize(400, 400);
window.show();
return app.exec();
}
glbuffertest.pro:
######################################################################
# Automatically generated by qmake (3.0) Fri May 16 09:49:41 2014
######################################################################
TEMPLATE = app
TARGET = glbuffertest
INCLUDEPATH += .
CONFIG += qt debug
# Input
SOURCES += glbuffertest.cpp glwindow.cpp
HEADERS += glwindow.h
更新:
我试图摆脱我的_matbo
缓冲区,而是将矩阵数据放入与位置和颜色属性相同的VBO中,但对我来说不起作用。我的initGL
函数现在如下:
void GLWindow::initGL()
{
setupShaders();
_program->bind();
_positionAttr = _program->attributeLocation("position");
_colourAttr = _program->attributeLocation("colour");
_matrixAttr = _program->attributeLocation("matrix");
QVector<QVector3D> triangles;
triangles << QVector3D(-0.5, 0.5, 1) << QVector3D(-0.5, -0.5, 1) << QVector3D(0.5, -0.5, 1);
triangles << QVector3D(0.5, 0.5, 0.5) << QVector3D(-0.5, -0.5, 0.5) << QVector3D(0.5, -0.5, 0.5);
QVector<QVector3D> colours;
colours << QVector3D(1, 0, 0) << QVector3D(0, 1, 0) << QVector3D(0, 0, 1);
colours << QVector3D(1, 1, 1) << QVector3D(1, 1, 1) << QVector3D(1, 1, 1);
_vao.create();
_vao.bind();
_vbo.create();
_vbo.setUsagePattern(QOpenGLBuffer::StaticDraw);
_vbo.bind();
size_t positionSize = triangles.size() * sizeof(QVector3D);
size_t colourSize = colours.size() * sizeof(QVector3D);
size_t matrixSize = 4 * sizeof(QVector4D);
_vbo.allocate(positionSize + colourSize + matrixSize);
_vbo.bind();
_vbo.write(0, triangles.constData(), positionSize);
_vbo.write(positionSize, colours.constData(), colourSize);
_colourOffset = positionSize;
_matrixOffset = positionSize + colourSize;
_program->setAttributeBuffer(_positionAttr, GL_FLOAT, 0, 3, 0);
_program->setAttributeBuffer(_colourAttr, GL_FLOAT, _colourOffset, 3, 0);
_program->setAttributeBuffer(_matrixAttr, GL_FLOAT, _matrixOffset, 4, 4 * sizeof(QVector4D));
_program->enableAttributeArray(_positionAttr);
_program->enableAttributeArray(_colourAttr);
_program->enableAttributeArray(_matrixAttr);
_func330->glVertexAttribDivisor(_matrixAttr, 1);
_vao.release();
_program->release();
resizeGL(width(), height());
}
和 paintGL
:
void GLWindow::paintGL()
{
if (! _context) // not yet initialized
return;
_context->makeCurrent(this);
QColor background(Qt::black);
glClearColor(background.redF(), background.greenF(), background.blueF(), 1.0f);
glClearDepth(1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
QMatrix4x4 matrix;
matrix.perspective(60, 4.0/3.0, 0.1, 100.0);
matrix.translate(0, 0, -2);
_program->bind();
_vao.bind();
_vbo.write(_matrixOffset, matrix.constData(), 4 * sizeof(QVector4D));
/* I tried replacing the three preceding lines with the following, without success: */
/*
_vao.bind();
_vbo.bind();
_vbo.write(_matrixOffset, matrix.constData(), 4 * sizeof(QVector4D));
_program->bind();
_program->enableAttributeArray(_matrixAttr);
_func330->glVertexAttribDivisor(_matrixAttr, 1); */
glEnable(GL_DEPTH_TEST);
_func330->glDrawArraysInstanced(GL_TRIANGLES, 0, 6, 1);
_vao.release();
_program->release();
_context->swapBuffers(this);
_context->doneCurrent();
}
看起来我的实例化问题不仅仅是在错误的时间绑定了错误的缓冲区。我还做错了什么?