【发布时间】：2019-08-07 04:45:35
【问题描述】：
我试图弄清楚如何将 OpenGL 与 QtQuickPaintedItem 一起使用。根据文档，这似乎是可能的，并且有几个“帮助”类。
我在下面尝试了这段代码，我还尝试创建 QOpenGLPaintDevice、QOpenGLContext 和 QOpenGLFramebufferObject 并将它们的实例以多种组合传递给它们的函数，但它也不起作用。
/// Simple3d.h
#ifndef SIMPLE3D_H
#define SIMPLE3D_H
#include<QtQuick/QQuickPaintedItem>
#include<QOpenGLFunctions>
// Not sure if I need to use any of these classes.
//#include<QOpenGLPaintDevice>
//#include<QOpenGLContext>
//#include<QOpenGLFramebufferObject>
//#include<QOpenGLShaderProgram>
//#include <GL/gl.h>
/** @brief inherets from QtQuickItem and it draws
* triangle.
*
*/
class Simple3d : public QQuickPaintedItem
{
Q_OBJECT
public:
/** Call this function to be able to instantiate this
* item in a QML file.
*/
static void register_qml_item();
Simple3d();
void paint(QPainter * painter) override;
virtual ~Simple3d() override;
private:
bool mDebug;
/** OpenGL stuff */
bool mOpenGlInitialized;
GLuint mProgramId;
static const GLuint mVertexArrayID = 0;
QOpenGLFunctions *mGlFuncs;
// Not sure when is a good time to update these:
GLsizei mWidth, mHeight;
GLuint load_shader(GLenum type, const char *shaderSrc);
void verify_initialized();
void draw_open_gl();
};
#endif
/// Simple3d.cpp
#include "simple3d.h"
#include <QSGGeometryNode>
#include <QSGVertexColorMaterial>
#include <QtMath>
#include<QOpenGLFunctions>
#include<QPainter>
#include<QGuiApplication>
using namespace std;
Simple3d::Simple3d()
{
mDebug = true;
mOpenGlInitialized = false;
mGlFuncs = nullptr;
setFlag(ItemHasContents, true);
}
void Simple3d::paint(QPainter *painter)
{
if (mDebug) qDebug("Simple3d is running paint()");
if (!mGlFuncs){
mGlFuncs = new QOpenGLFunctions();
mGlFuncs->initializeOpenGLFunctions();
}
painter->beginNativePainting();
verify_initialized();
draw_open_gl();
painter->endNativePainting();
if (mDebug) qDebug("Simple3d finished rendering.");
}
GLuint Simple3d::load_shader(GLenum type, const char *shaderSrc)
{
GLuint shader;
GLint compiled;
// Create the shader object
shader = mGlFuncs->glCreateShader(type);
if(shader == 0)
return 0;
// Load the shader source
mGlFuncs->glShaderSource(shader, 1, &shaderSrc, nullptr);
// Compile the shader
mGlFuncs->glCompileShader(shader);
// Check the compile status
mGlFuncs->glGetShaderiv(shader, GL_COMPILE_STATUS, &compiled);
if(!compiled)
{
GLint infoLen = 0;
mGlFuncs->glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &infoLen);
if(infoLen > 1)
{
char* infoLog = new char[size_t(infoLen)+1];
mGlFuncs->glGetShaderInfoLog(shader, infoLen, nullptr, infoLog);
qDebug("In the shader source:\n%s", shaderSrc);
qDebug("Error compiling shader:\n%s\n", infoLog);
delete [] infoLog;
}
mGlFuncs->glDeleteShader(shader);
return 0;
}
return shader;
}
void Simple3d::verify_initialized()
{
if (mOpenGlInitialized) return;
// This piece is partially taken from:
// https://www.khronos.org/assets/uploads/books/openglr_es_20_programming_guide_sample.pdf
mWidth = 50;
mHeight = 50;
const char vShaderStr[] =
"attribute vec4 vPosition;\n"
"void main()\n"
"{\n"
" gl_Position = vPosition;\n"
"}\n";
const char fShaderStr[] =
"//precision mediump float;\n"
"void main()\n"
"{\n"
" gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0); \n"
"}\n";
GLuint vertexShader;
GLuint fragmentShader;
GLint linked;
// Load the vertex/fragment shaders
vertexShader = load_shader(GL_VERTEX_SHADER, vShaderStr);
fragmentShader = load_shader(GL_FRAGMENT_SHADER, fShaderStr);
// Create the program object
mProgramId = mGlFuncs->glCreateProgram();
if(mProgramId == 0) {
qDebug("Failed to create the OpenGL program.");
return;
}
mGlFuncs->glAttachShader(mProgramId, vertexShader);
mGlFuncs->glAttachShader(mProgramId, fragmentShader);
// Bind vPosition to attribute 0
mGlFuncs->glBindAttribLocation(mProgramId, mVertexArrayID, "vPosition");
// Link the program
mGlFuncs->glLinkProgram(mProgramId);
// Check the link status
mGlFuncs->glGetProgramiv(mProgramId, GL_LINK_STATUS, &linked);
if(!linked)
{
qDebug("Failed to link OpenGL program.");
GLint infoLen = 0;
mGlFuncs->glGetProgramiv(mProgramId, GL_INFO_LOG_LENGTH, &infoLen);
if(infoLen > 1)
{
char* infoLog = new char[size_t(infoLen)];
mGlFuncs->glGetProgramInfoLog(mProgramId, infoLen, nullptr, infoLog);
qDebug("Error linking program:\n%s\n", infoLog);
delete [] infoLog;
}
mGlFuncs->glDeleteProgram(mProgramId);
return;
}
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
mOpenGlInitialized = true;
qDebug("OpenGL was initialized successfully.");
return;
}
void Simple3d::draw_open_gl()
{
if (!mOpenGlInitialized){
QGuiApplication::exit(1);
return;
}
mGlFuncs->glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
mGlFuncs->glEnable(GL_DEPTH_TEST);
mGlFuncs->glUseProgram(mProgramId);
GLfloat vVertices[] =
{0.0f, 0.5f, 0.0f,
-0.5f, -0.5f, 0.0f,
0.5f, -0.5f, 0.0f};
// Set the viewport
mGlFuncs->glViewport(0, 0, mWidth, mHeight);
// Clear the color buffer
glClear(GL_COLOR_BUFFER_BIT);
// Load the vertex data
mGlFuncs->glVertexAttribPointer(mVertexArrayID, 3, GL_FLOAT, GL_FALSE, 0, vVertices);
mGlFuncs->glEnableVertexAttribArray(0);
mGlFuncs->glDrawArrays(GL_TRIANGLES, 0, 3);
mGlFuncs->glFlush();
mGlFuncs->glFinish();
mGlFuncs->glUseProgram(0); // release the program.
}
Simple3d::~Simple3d()
{
}
void Simple3d::register_qml_item()
{
qmlRegisterType<Simple3d>("CustomGraphicsItems", 1, 0, "Simple3d");
}
/// main.cpp
#include "simple3d.h"
#include <stdexcept>
using namespace std;
int main(int argc, char *argv[]){
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QGuiApplication app(argc, argv);
Simple3d::register_qml_item();
QQmlApplicationEngine engine;
const QUrl url(QStringLiteral("qrc:/example_Simple3d.qml"));
QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
&app, [url](QObject *obj, const QUrl &objUrl)
{
if (!obj && url == objUrl)
QCoreApplication::exit(-1);
}, Qt::QueuedConnection);
engine.load(url);
int num_root_objects = engine.rootObjects().size();
qDebug("The number of root objects: %i", num_root_objects);
if (engine.rootObjects().size()!=1){
throw logic_error("Expected exactly one root object"
"in the qml file");
}
QObject * root = engine.rootObjects()[0];
Simple3d * draw_3d_item = root->findChild<Simple3d*>("draw_3d_item");
if (!draw_3d_item){
throw logic_error("Did not find item 'draw_3d_item'.");
}
int result = app.exec();
qDebug("The app is exiting.");
return result;
}
/// example_Simple3d.qml
import QtQuick 2.12
import QtQuick.Window 2.12
import CustomGraphicsItems 1.0
import QtQuick.Layouts 1.12
import QtQuick.Controls 2.12
Window {
visible: true
Simple3d{
id: draw_3d_item
width: 50
height: 50
anchors.fill: parent
objectName: "draw_3d_item"
}
}
代码应该在黑色背景上显示一个红色三角形，但没有绘制任何内容。
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