Convert Coin3D SoOffscreenRenderer to QImage and render with OpenGL - c++

Question

I'm trying to display a Coin3D/Open Inventor scene with QT in a QGLWidget, by using the SoOffscreenRenderer and I need help converting it to a QImage
What I tried so far, is render the scene into SoOffscreenRenderer and get the buffer like this:
unsigned char * getCoinCubeImgBuffer(){
// [...] create the scene, add lightning and camera
SoOffscreenRenderer offscreenRenderer(vpRegion);
offscreenRenderer.setComponents(
SoOffscreenRenderer::Components::RGB_TRANSPARENCY
);
SbBool ok = offscreenRenderer.render(root);
// to be sure that something is actually rendered
// save the buffer content to a file
SbBool ok = offscreenRenderer.render(root);
qDebug() << "SbBool ok?" << ok;
qDebug() << "wasFileWrittenRGB" <<
offscreenRenderer.writeToRGB("C:/test-gl.rgb");
qDebug() << "wasFileWrittenPS" <<
offscreenRenderer.writeToPostScript("C:/test-gl.ps");
unsigned char * imgbuffer = offscreenRenderer.getBuffer();
return imgbuffer;
}
and then create a QImage from the buffer data:
QImage convertImgBuffer(){
unsigned char *const imgBuffer = getCoinCubeImgBuffer();
QImage img(imgBuffer, windowWidth, windowHeight, QImage::Format_ARGB32);
// Important!
img = img.rgbSwapped();
QImage imgGL = convertToGLFormat(img);
return imgGL;
}
Would this be the correct way to do it?
As described in this question about drawing a QImage, I'm able to draw it if the source is a picture.
e: To make sure that my buffer actually contains a scene, I write the buffer content to two files. You can view .rgb and .ps files for example with IrfanView plus its plugins.
e2: Just figured out, that I have to use img.rgbSwapped(). Now it's showing the scene black&white and without lightning. I will investigate further.
e3: With the code like this, you need to adapt the OpenGL call in this way to render in color
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, tex.width(),
tex.height(), 0, GL_RGBA, GL_UNSIGNED_BYTE, tex.bits());
First format is GL_RGB, second GL_RGBA. The cube is still completely black though.
e4: It was an error in my scene, you have to add a light before you add the rest and especially before you add the camera.
So now I can either use `QGLWidget`s functions like `bindTexture()` or use direct OpenGL calls, but I'm not sure how exactly. It would be great if someone could push me in the right direction.
Can't I just use OpenGL like this?
glEnable(GL_TEXTURE_2D);
glGenTextures(1, &offscreenBufferTexture);
glBindTexture(GL_TEXTURE_2D, offscreenBufferTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, imgGL.width(),
imgGL.height(), 0, GL_RGBA, GL_UNSIGNED_BYTE,
imgGL.bits());
Or maybe `glDrawPixels()`?
glDrawPixels(imgGL.width(), imgGL.height(), GL_RGBA,
GL_UNSIGNED_BYTE, imgGL.bits());
I figured out how to draw a QImage with OpenGL, see this thread. So there seems to be a problem with the buffer or the conversion of it.

Answer 1

Here's the resulting code which renders the scene correctly.
First create a valid scene
void loadCoinScene(){
// Init Coin
SoDB::init();
// The root node
root = new SoSeparator;
root->ref();
// Add the light _before_ you add the camera
SoDirectionalLight * light = new SoDirectionalLight;
root->addChild(light);
vpRegion.setViewportPixels(0, 0, coinSceneWidth, coinSceneHeight);
SoPerspectiveCamera *perscam = new SoPerspectiveCamera();
root->addChild(perscam);
SbRotation cameraRotation = SbRotation::identity();
cameraRotation *= SbRotation(SbVec3f(0, 1, 0), 0.4f);
perscam->orientation = cameraRotation;
SoCube * cube = new SoCube;
root->addChild(cube);
// make sure that the cube is visible
perscam->viewAll(root, vpRegion);
}
Then render the scene into the Offscreen Buffer and convert it to a QImage:
QImage getCoinCubeImgBuffer(){
SoOffscreenRenderer offscreenRenderer(vpRegion);
offscreenRenderer.setComponents(
SoOffscreenRenderer::Components::RGB_TRANSPARENCY
);
offscreenRenderer.render(root);
QImage img(offscreenRenderer.getBuffer(), coinSceneWidth,
coinSceneHeight, QImage::Format_ARGB32);
// Important!
return img.rgbSwapped();
}
If you now want to render the QImage with OpenGL, use my solution from my Render QImage with OpenGL question and change the loadTexture2() method to this:
QImage loadTexture2(GLuint &textureID){
glEnable(GL_TEXTURE_2D); // Enable texturing
glGenTextures(1, &textureID); // Obtain an id for the texture
glBindTexture(GL_TEXTURE_2D, textureID); // Set as the current texture
QImage im = getCoinCubeImgBuffer();
// Convert to OpenGLs unnamed format
// The resulting GL format is GL_RGBA
QImage tex = QGLWidget::convertToGLFormat(im);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, tex.width(), tex.height(), 0,
GL_RGBA, GL_UNSIGNED_BYTE, tex.bits());
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
glDisable(GL_TEXTURE_2D);
return tex;
}

Answer 2

I don't think there is a need to feed the texture through QImage. The following is a working example:
#include <QApplication>
#include <QGLWidget>
#include <Inventor/SoInput.h>
#include <Inventor/SoOffscreenRenderer.h>
#include <Inventor/nodes/SoSeparator.h>
static GLuint textureID(0);
class GLWidget : public QGLWidget
{
public:
explicit GLWidget() : QGLWidget() {}
~GLWidget() {}
protected:
void initializeGL() {
glShadeModel(GL_FLAT);
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
static GLfloat lightAmbient[4] = { 1.0, 1.0, 1.0, 1.0 };
glLightfv(GL_LIGHT0, GL_AMBIENT, lightAmbient);
}
void paintGL() {
if (!textureID)
return;
glClearColor(0.4f, 0.1f, 0.1f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, textureID);
glBegin(GL_QUADS);
glTexCoord2f(0,0); glVertex3f(-1, -1, -1);
glTexCoord2f(1,0); glVertex3f( 1, -1, -1);
glTexCoord2f(1,1); glVertex3f( 1, 1, -1);
glTexCoord2f(0,1); glVertex3f(-1, 1, -1);
glEnd();
glDisable(GL_TEXTURE_2D);
}
void resizeGL(int width, int height) {
int side = qMin(width, height);
glViewport((width - side) / 2, (height - side) / 2, side, side);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-1.0, 1.0, -1.0, 1.0, 0.0, 1000.0);
glMatrixMode(GL_MODELVIEW);
}
};
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
GLWidget glWidget;
glWidget.show();
static const char * inlineSceneGraph[] = {
"#Inventor V2.1 ascii\n",
"\n",
"Separator {\n",
" PerspectiveCamera { position 0 0 5 }\n",
" DirectionalLight {}\n",
" Rotation { rotation 1 0 0 0.3 }\n",
" Cone { }\n",
" BaseColor { rgb 1 0 0 }\n",
" Scale { scaleFactor .7 .7 .7 }\n",
" Cube { }\n",
"\n",
" DrawStyle { style LINES }\n",
" ShapeHints { vertexOrdering COUNTERCLOCKWISE }\n",
" Coordinate3 {\n",
" point [\n",
" -2 -2 1.1, -2 -1 1.1, -2 1 1.1, -2 2 1.1,\n",
" -1 -2 1.1, -1 -1 1.1, -1 1 1.1, -1 2 1.1\n",
" 1 -2 1.1, 1 -1 1.1, 1 1 1.1, 1 2 1.1\n",
" 2 -2 1.1, 2 -1 1.1, 2 1 1.1, 2 2 1.1\n",
" ]\n",
" }\n",
"\n",
" Complexity { value 0.7 }\n",
" NurbsSurface {\n",
" numUControlPoints 4\n",
" numVControlPoints 4\n",
" uKnotVector [ 0.0, 0.0, 0.0, 0.0, 1.0, 1.0, 1.0, 1.0 ]\n",
" vKnotVector [ 0.0, 0.0, 0.0, 0.0, 1.0, 1.0, 1.0, 1.0 ]\n",
" }\n",
"}\n",
NULL
};
SoInput in;
in.setStringArray(inlineSceneGraph);
glWidget.resize(600, 600);
SoOffscreenRenderer renderer(SbViewportRegion(glWidget.width(),
glWidget.height()));
renderer.setComponents(SoOffscreenRenderer::RGB_TRANSPARENCY);
renderer.setBackgroundColor(SbColor(.0f, .0f, .8f));
SoSeparator *rootScene = SoDB::readAll(&in);
rootScene->ref();
renderer.render(rootScene);
rootScene->unref();
glEnable(GL_TEXTURE_2D); // Enable texturing
glGenTextures(1, &textureID); // Obtain an id for the texture
glBindTexture(GL_TEXTURE_2D, textureID); // Set as the current texture
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA,
renderer.getViewportRegion().getViewportSizePixels()[0],
renderer.getViewportRegion().getViewportSizePixels()[1],
0, GL_BGRA, GL_UNSIGNED_BYTE, renderer.getBuffer());
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
glDisable(GL_TEXTURE_2D);
return app.exec();
}

Answer 3

A simple example of rendering a local scene with SoWin, Coin3D ( download SoWin from here )
SoSeparator * CreateScene(SoSeparator* root)
{
root->ref();
root->setName("root_node");
SoPerspectiveCamera * camera = new SoPerspectiveCamera;
camera->setName("simple_camera");
SbRotation cameraRotation = SbRotation::identity();
cameraRotation *= SbRotation(SbVec3f(1, 0, 0), -0.4f);
cameraRotation *= SbRotation(SbVec3f(0, 1, 0), 0.4f);
camera->orientation = cameraRotation;
SoCone* cone1= new SoCone();
cone1->setName("Cone1");
SoBaseColor * color = new SoBaseColor;
color->setName("myColor");
root->addChild(camera);
root->addChild(cone1);
root->addChild(color);
return root;
}
Render scene created above
void RenderLocal()
{
HWND window = SoWin::init("IvExample");
if (window==NULL) exit(1);
SoWinExaminerViewer * viewer = new SoWinExaminerViewer(window);
SoSeparator * root = new SoSeparator;
auto* data = CreateScene(root);
data->getNumChildren();
viewer->setSceneGraph(root);
viewer->show();
SoWin::show(window);
SoWin::mainLoop();
delete viewer;
root->unref();
}
Render scene from iv file
int RenderFile()
{
HWND window = SoWin::init("Iv");
if (window==NULL) exit(1);
SoWinExaminerViewer * viewer = new SoWinExaminerViewer(window);
SoInput sceneInput;
if ( !sceneInput.openFile( "example.iv" ) )
return -1;
if ( !sceneInput.openFile(cPath) )
return -1;
SoSeparator *root =SoDB::readAll( &sceneInput );
root->ref();
viewer->setSceneGraph(root);
viewer->show();
SoWin::show(window);
SoWin::mainLoop();
delete viewer;
}