Jie Liu wrote:
> Hi,
>
> I want to use OpenSG do display about 150 images located in a given
> directory.
> For each time, I show one of them, and I press left key or right key to
> nevigate backward or forward. All images should align center, keep their
> width/height (w/h) ratio and they will fit to the width or height of the
> window according to the value of w/h ratio.
>
> I now have three solutions for this purpose.
> a). take an image as a background object. The problem is OpenSG will
> auto scale the image to the window area for me. But as I must keep the
> width/height ratio of the image, I give up.
That's just how the default ImageBackground works currently. Adding
aspect-keeping functionality would be a welcome patch though. :)
> b). take an image as a foreground object, the problem is I can only
> appoint its bottom-left position. There seems no parameters for me to
> scale its size.
IIRC, I'm not sure OpenGL can scale images uploaded with glWritePixels,
so that would be OpenGL's fault, not OpenSG's. :)
> Below are my code to do this
> ===================================================================
> ImagePtr tImage = Image::create();
> *tImage->read(file_name[index]);* *// I change the value of /index/
> to display different images. Images are loaded dynamically according to
> their names*
>
> ImageForegroundPtr ptrImgForeground = ImageForeground::create();
> beginEditCP(ptrImgForeground);
> {
> * ptrImgForeground->addImage(tImage, Pnt2f(0.0, 0)); // Can I
> assign a bounding box for an image? Or do I have to manually scale the
> image first?*
> }
> endEditCP(ptrImgForeground);
>
> * g_ptrViewport->getMFForegrounds()->push_back(ptrImgForeground); *
> *// push_back is to add a new image to the queue, OpenSG will try to
> render all images in the queue and this will slow down the rendering
> speed obviously. But I only want to display a single image at one time.
> So what is the right and efficient way to replace the current foreground
> image?
g_ptrViewport->getMFForegrounds()[0] = ptrImgForeground;
> *================================================================
>
> c). Take an image as a texture material, and attach it to a Quad primitive.
> ================================================================
> ImagePtr tImage = Image::create();
> tImage->read(file_name[index]);
>
> beginEditCP(g_ptrGeoTex);
> g_ptrGeoTex->setImage(tImage); *// g_ptrGeoTex is a globle variable,
> its type is SimpleTexturedMaterialPtr*
> endEditCP(g_ptrGeoTex);
>
> beginEditCP(g_ptrGeoQuad);
> g_ptrGeoQuad->setMaterial(g_ptrGeoTex);* // I found the
> setMaterial process will be very very slow, how can I accelerate it?*
You're probably suffering from auto mipmap generation here. (Mipmapping
for textures is enabled by default, and if you set an image with no
mipmaps, OpenSG creates them for you whe you use the material for the
first time). Try setting the minification filter (minFilter) to GL_LINEAR.
> endEditCP(g_ptrGeoQuad);
> ================================================================
>
> So, what is your suggestion to write such a program?
If you have enough memory (system and gfx) textures is probably the way
to go, because you can do more fun stuff with them (animation etc).
If not, you probably need to use ImageBackground or ImageForeground, but
neither of these do what you want currently, so you need to hack them a
bit. If you know OpenGL well enough to do get it to do what you want,
this is pretty easy. (I haven't looked at that part of OpenGL for a
time, so I can't say if nor how it can and should be done. Maybe some
other guys know better).
> I also want to load
> all iamges at the begining of the program and store them in vectors
> (vector<ImagePtr>, and vector<SimpleTexturedMaterialPtr>), but the
> program crashed while switching the image. What is the right way to read
> and store all image data?
You probably want Image|MaterialRefPtr to make sure your images stay in
memory here. However, make sure your images fit in graphics memory if
you use textures.
> The email is a little long, I hope it will not bother you too much~
Not at all. Glad to help. :)
Cheers,
/Marcus
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