我试图编写一个通过OpenGL将纹理渲染成QML项目的应用程序。在网上搜索并尝试各种各样的事情之后（感觉好像很多猜测，我对OpenGl的理解非常有限），我最终通过Valgrind运行程序并发现了非法的内存访问，这意味着我没有初始化所需的一切为OpenGl绘制正确。我希望有人可以查看我的粗略代码并告诉我我忘记了哪一步。
我尝试关注并合并QT文档中的两个教程，其中一个（http://doc.qt.io/qt-5/qtquick-scenegraph-openglunderqml-example.html）显示QML和OpenGl，以及此一个（http://doc.qt.io/qt-5/qtopengl-textures-example.html），其中显示了如何呈现纹理使用OpenGl和QT。我稍微改了一下，因为我的纹理只是我希望显示的二维图像。我能够成功地跟随后者，将我的纹理渲染到视口并将其绘制在屏幕上，不幸的是，当尝试集成QML时，事情变得艰难。
我的绘画功能如下：
void glViewer::paint()
{
// program is type QOpenGLShaderProgram *
if (!program) initializeGL();
if (!program->bind()) std::cerr << "Error: Program failed to bind\n";
glViewport(0, 0, _viewportSize.width(), _viewportSize.height());
glClearColor(clearColor.redF(), clearColor.greenF(), clearColor.blackF(), clearColor.alphaF());
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
QMatrix4x4 m;
m.ortho(0.0f, 1.0f, 1.0f, 0.0f, 4.0f, 15.0f);
m.translate(0.0f, 0.0f, -10.0f);
program->setUniformValue("matrix", m);
program->enableAttributeArray(PROGRAM_VERTEX_ATTRIBUTE);
program->enableAttributeArray(PROGRAM_TEXCOORD_ATTRIBUTE);
program->setAttributeBuffer(PROGRAM_VERTEX_ATTRIBUTE, GL_FLOAT, 0, 3, 5 * sizeof(GLfloat));
program->setAttributeBuffer(PROGRAM_TEXCOORD_ATTRIBUTE, GL_FLOAT, 3 * sizeof(GLfloat), 2, 5 * sizeof(GLfloat));
texture->bind();
glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
program->disableAttributeArray(PROGRAM_VERTEX_ATTRIBUTE);
program->disableAttributeArray(PROGRAM_TEXCOORD_ATTRIBUTE);
program->release();
// _window refers the QQuickWindow generated by the QApplication
_window->resetOpenGLState();
}
如果没有着色器程序，第一行调用intializeGL（），这是我认为问题所在。该功能定义如下：
void glViewer::initializeGL()
{
initializeOpenGLFunctions();
texture = new QOpenGLTexture(QOpenGLTexture::Target2D);
texture->setSize(imageDisplayResolution.x,imageDisplayResolution.y,1);
texture->setMinMagFilters(QOpenGLTexture::Nearest, QOpenGLTexture::Nearest);
texture->setWrapMode(QOpenGLTexture::ClampToBorder);
texture->setFormat(QOpenGLTexture::TextureFormat::R32F);
texture->allocateStorage(QOpenGLTexture::Luminance, QOpenGLTexture::Float32);
if (!texture->isStorageAllocated()) std::cerr << "Error: Failed to allocate texture!\n";
QVector<GLfloat> vertData;
// vertex position
vertData.append(0);
vertData.append(0);
vertData.append(0);
// texture coordinate
vertData.append(0);
vertData.append(0);
// vertex position
vertData.append(0);
vertData.append(1);
vertData.append(0);
// texture coordinate
vertData.append(0);
vertData.append(1);
// vertex position
vertData.append(1);
vertData.append(1);
vertData.append(0);
// texture coordinate
vertData.append(1);
vertData.append(1);
// vertex position
vertData.append(1);
vertData.append(0);
vertData.append(0);
// texture coordinate
vertData.append(1);
vertData.append(0);
vbo.create();
if (!vbo.bind()) std::cerr << "Error: VBO bind has failed\n";
vbo.allocate(vertData.constData(), vertData.count() * sizeof(GLfloat));
// Enable or disable server-side GL capabilities.
glEnable(GL_DEPTH_TEST);
glEnable(GL_CULL_FACE);
#define PROGRAM_VERTEX_ATTRIBUTE 0
#define PROGRAM_TEXCOORD_ATTRIBUTE 1
program = new QOpenGLShaderProgram;
if (!program->addShaderFromSourceCode(QOpenGLShader::Vertex,
"attribute highp vec4 vertex;\n"
"attribute mediump vec4 texCoord;\n"
"varying mediump vec4 texc;\n"
"uniform mediump mat4 matrix;\n"
"void main(void)\n"
"{\n"
" gl_Position = matrix * vertex;\n"
" texc = texCoord;\n"
"}\n")) { std::cerr << "Error: Vertex shader failed to compile!\n"; }
if (!program->addShaderFromSourceCode(QOpenGLShader::Fragment,
"uniform sampler2D texture;\n"
"varying mediump vec4 texc;\n"
"void main(void)\n"
"{\n"
" gl_FragColor = texture2D(texture, texc.st).rrra;\n"
"}\n")) { std::cerr << "Error: Fragment shader failed to compile!\n"; }
// Binds the attribute name to the specified location.
program->bindAttributeLocation("vertex", PROGRAM_VERTEX_ATTRIBUTE);
program->bindAttributeLocation("texCoord", PROGRAM_TEXCOORD_ATTRIBUTE);
if (!program->link()) std::cerr << "Error: Program shaders failed to link\n";
if (!program->bind()) std::cerr << "Error: Program failed to bind\n";
program->setUniformValue("texture", 0);
}
paint（）是连接到QQuickWindow :: beforeRendering信号的插槽。使用调试器逐步调试告诉我，当调用paint（）时，所有指针（纹理，程序）都不为null。没有OpenGL调用抛出错误，程序只是在glDrawArrays上的paint（）中段错误。
谢谢！
编辑：进一步的调试告诉我它已成功通过绘画功能一次，它在第二次通过它失败。但是，我从未看到完全绘制的纹理，只填写了应用程序背景。
答案 0 :(得分：0)
paint函数应该写成如下以保持状态并防止绘图上的段错误：
if (!program) initializeGL();
program->bindAttributeLocation("vertex", PROGRAM_VERTEX_ATTRIBUTE);
program->bindAttributeLocation("texCoord", PROGRAM_TEXCOORD_ATTRIBUTE);
if (!program->bind()) std::cerr << "Error: Program failed to bind\n";
texture->bind();
vbo.bind();
glClearColor(_clearColor.redF(), _clearColor.greenF(), _clearColor.blackF(), _clearColor.alphaF());
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glViewport(viewportPosition.x(), viewportPosition.y(), viewportSize.width(), viewportSize.height());
QMatrix4x4 m;
m.ortho(0.0f, 1.0f, 1.0f, 0.0f, 4.0f, 15.0f);
m.translate(0.0f, 0.0f, -10.0f);
program->setUniformValue("matrix", m);
program->setUniformValue("texture", 0);
program->enableAttributeArray(PROGRAM_VERTEX_ATTRIBUTE);
program->enableAttributeArray(PROGRAM_TEXCOORD_ATTRIBUTE);
program->setAttributeBuffer(PROGRAM_VERTEX_ATTRIBUTE, GL_FLOAT, 0, 3, 5 * sizeof(GLfloat));
program->setAttributeBuffer(PROGRAM_TEXCOORD_ATTRIBUTE, GL_FLOAT, 3 * sizeof(GLfloat), 2, 5 * sizeof(GLfloat));
glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
program->disableAttributeArray(PROGRAM_VERTEX_ATTRIBUTE);
program->disableAttributeArray(PROGRAM_TEXCOORD_ATTRIBUTE);
program->disableAttributeArray(0);
program->release();
texture->release();
vbo.release();
_window->resetOpenGLState();