我的 OpenGL QQuickItem 没有我想要的大小

我在Qtquick上使用OpenGL绘图，无论我在QML上OpenGlVideoQtQuick上放什么尺寸，它总是占据窗口的整个空间。我希望能够控制它的大小。

我创建了这个最小的示例，它使用 OpenGL 绘制绿屏。我应该能够控制 QQuickItem 的大小，从而控制绿屏的大小，例如占据屏幕的 1/4。

你可以看到我甚至在QQuickItem上尝试(并评论)了setWidth和setHeight方法。这是行不通的。

您可以在此处看到一个最小工作且可编译的示例：https://github.com/lucaszanella/openglqtquickexample/tree/4de3ec1535eb40c31788512a027c1e86f76d4090

如何控制我的QQuickItem的大小？

main.qml：

import QtQuick 2.0
import OpenGLComponents 1.0
Item {
width: 1280
height: 720
OpenGlVideoQtQuick {
width: 640
height: 480
}
}

主.cpp：

#include <iostream>
#include <QApplication>
#include <QMediaPlayer>
#include <QPushButton> 
#include <QGuiApplication>
#include <QtQuick/QQuickView>
#include "OpenGlVideoQtQuick.h"
int main(int argc, char **argv)
{
QGuiApplication app(argc, argv);
QCoreApplication::addLibraryPath("./");
qmlRegisterType<OpenGlVideoQtQuick>("OpenGLComponents", 1, 0, "OpenGlVideoQtQuick");
QQuickView view;
view.setResizeMode(QQuickView::SizeRootObjectToView);
view.setSource(QUrl("qrc:/main.qml"));
view.show();
return app.exec();
}

OpenGlVideoQtQuick.cpp：

#include "OpenGlVideoQtQuick.h"
#define GET_STR(x) #x
#define A_VER 3
#define T_VER 4
//Simple shader. Outpus the same location as input, I guess
const char *vString2 = GET_STR(
attribute vec4 vertexIn;
attribute vec2 textureIn;
varying vec2 textureOut;
void main(void)
{
gl_Position = vertexIn;
textureOut = textureIn;
}
);
const char *tString2 = GET_STR(
varying vec2 textureOut;
uniform sampler2D tex_y;
uniform sampler2D tex_u;
uniform sampler2D tex_v;
void main(void)
{
vec3 yuv;
vec3 rgb;
yuv.x = texture2D(tex_y, textureOut).r;
yuv.y = texture2D(tex_u, textureOut).r - 0.5;
yuv.z = texture2D(tex_v, textureOut).r - 0.5;
rgb = mat3(1.0, 1.0, 1.0,
0.0, -0.39465, 2.03211,
1.13983, -0.58060, 0.0) * yuv;
gl_FragColor = vec4(rgb, 1.0);
}
);
OpenGlVideoQtQuick::OpenGlVideoQtQuick():
openGlVideoQtQuickRenderer(nullptr)
{
connect(this, &QQuickItem::windowChanged, this, &OpenGlVideoQtQuick::handleWindowChanged);
update();
//setWidth(640);
//setHeight(480);
//width=640
//height=480
}
void OpenGlVideoQtQuick::handleWindowChanged(QQuickWindow *win)
{
if (win) {
connect(win, &QQuickWindow::beforeSynchronizing, this, &OpenGlVideoQtQuick::sync, Qt::DirectConnection);
win->setClearBeforeRendering(false);
}
}
void OpenGlVideoQtQuick::update()
{
if (window())
window()->update();
}

OpenGlVideoQtQuickRenderer::~OpenGlVideoQtQuickRenderer()
{
delete program;
}

void OpenGlVideoQtQuick::sync()
{
if (!openGlVideoQtQuickRenderer) {
openGlVideoQtQuickRenderer = new OpenGlVideoQtQuickRenderer();
connect(window(), &QQuickWindow::beforeRendering, openGlVideoQtQuickRenderer, &OpenGlVideoQtQuickRenderer::render, Qt::DirectConnection);
connect(window(), &QQuickWindow::afterRendering, this, &OpenGlVideoQtQuick::update, Qt::DirectConnection);
}
}
static const GLfloat ver[] = {
-1.0f,-1.0f,
1.0f,-1.0f,
-1.0f, 1.0f,
1.0f, 1.0f
};
static const GLfloat tex[] = {
0.0f, 1.0f,
1.0f, 1.0f,
0.0f, 0.0f,
1.0f, 0.0f
};

void OpenGlVideoQtQuickRenderer::render()
{
if (this->firstRun) {
std::cout << "Creating QOpenGLShaderProgram " << std::endl;
this->firstRun = false;
program = new QOpenGLShaderProgram();
initializeOpenGLFunctions();
std::cout << "Fragment Shader compilation: " << program->addShaderFromSourceCode(QOpenGLShader::Fragment, tString2) << std::endl;
std::cout << "Vertex Shader compilation: " << program->addShaderFromSourceCode(QOpenGLShader::Vertex, vString2) << std::endl;
program->bindAttributeLocation("vertexIn",A_VER);
program->bindAttributeLocation("textureIn",T_VER);
std::cout << "program->link() = " << program->link() << std::endl;
glGenTextures(3, texs);//TODO: ERASE THIS WITH glDeleteTextures
}
program->bind();
//glViewport(50, 50, 50, 50);
glVertexAttribPointer(A_VER, 2, GL_FLOAT, 0, 0, ver);
glEnableVertexAttribArray(A_VER);
glVertexAttribPointer(T_VER, 2, GL_FLOAT, 0, 0, tex);
glEnableVertexAttribArray(T_VER);
unis[0] = program->uniformLocation("tex_y");
unis[1] = program->uniformLocation("tex_u");
unis[2] = program->uniformLocation("tex_v");
//Y
glBindTexture(GL_TEXTURE_2D, texs[0]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, width, height, 0, GL_RED, GL_UNSIGNED_BYTE, 0);
//U
glBindTexture(GL_TEXTURE_2D, texs[1]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, width/2, height / 2, 0, GL_RED, GL_UNSIGNED_BYTE, 0);
//V
glBindTexture(GL_TEXTURE_2D, texs[2]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, width / 2, height / 2, 0, GL_RED, GL_UNSIGNED_BYTE, 0);

glDrawArrays(GL_TRIANGLE_STRIP,0,4);
program->disableAttributeArray(A_VER);
program->disableAttributeArray(T_VER);
program->release();
}