I'm trying to create a display with a complex OpenGL image and some spinboxes on the image. Using http://doc.qt.digia.com/qq/qq26-openglcanvas.html I'm able to have a two layers object (inheriting from QGraphicsScene) with a simple OpenGL image as background and the controls on foreground.
So, now I'm trying to display my true OpenGL image as background. This image is created by:
A quad mapped on a structure,
Some small 2D objects represented by 2D textures with alpha channel and specific shaders, drawn on the quad (upper z value)
Some polylines.
With this image I have some strange behavior. The 2D textured objects are drawn with a white background. Some experiments seem to indicate that, in the drawing of this complex OpenGL image the alpha channel is disabled.
I tried different configurations for the QGLWidget used as viewport of the QGraphicsView but without result.
So I need help to be able to create this OpenGL image with the right transparency effects.
Related
I'm coding a programm in C++ with glut, rendering a 3D model in a window.
I'm using glReadPixels to get the image of the scenery displayed in the windows.
And I would like to know how I can get, for a specific pixel (x, y), not directly its color but the color of the next object behind.
If I render a blue triangle, and a red triangle in front of it, glReadPixels gives me red colors from the red triangle.
I would like to know how I can get the colors from the blue triangle, the one I would get from glReadPixels if the red triangle wasn't here.
The default framebuffer only retains the topmost color. To get what you're suggesting would require a specific rendering pipeline.
For instance you could:
Create an offscreen framebuffer of the same dimensions as your target viewport
Render a depth-only pass to the offscreen framebuffer, storing the depth values in an attached texture
Re-render the scene with a special shader that only drew pixels where the post-transformation Z values was LESS than the value in the previously recorded depth buffer
The final result of the last render should be the original scene with the top layer stripped off.
Edit:
It would require only a small amount of new code to create the offscreen framebuffer and render a depth only version of the scene to it, and you could use your existing rendering pipeline in combination with that to execute steps 1 and 2.
However, I can't think of any way you could then re-render the scene to get the information you want in step 3 without a shader, because it both the standard depth test plus a test against the provided depth texture. That doesn't mean there isn't one, just that I'm not well versed in GL tricks to think of it.
I can think of other ways of trying to accomplish the same task for specific points on the screen by fiddling with the rendering system, but they're all far more convoluted than just writing a shader.
I am doing video texturing to a rectangle surface created. I need to create 2 more rectangle of say different size and then copy a part of the texturing video running on the 1st surface (for eg: middle part of the video ) and play it on the new surface created. Is this possible using OpenGL ES ? Through my native video surface renderer, I can do this functionality and can map it to OGLES application. I was just wondering whether it is possible to do directly from OGL app itself, by copying selected rectangle from one of the video texturing surface ?
If your texture is full motion video, you should not copy the texture data because that will be too slow too keep up with video frame rates. You should avoid using glTexImage2D() and instead use the EGL Image Extensions as detailed in my third article here:
http://montgomery1.com/opengl/
But either way, once you have the image in a texture and the texture is bound with glBindTexture(), then any number of rectangles you draw will be textured with that same currently-bound texture, without more copying. These rectangles are actually geometry constructed of triangles and not "surfaces". The framebuffer is the surface. The texture coordinates can be different for each rectangle, which allows you to crop and/or scale the texture mapping uniquely for each.
I need some help in surface area selection on a 3d model rendered in opengl by picking points through mouse. I know how to get a point in world coordinate but cant find a way to select an area. Later I need to remesh that selected area and map an image over it which I know.
Well, OpenGL by itself can't help you there. OpenGL is a drawing API. You draw things, but once the drawing commands have been executed all that's left are pixels in a framebuffer and OpenGL has no recollection about the geometry whatsoever.
You can use OpenGL to implement image based area selection algorithms, for example by drawing each face with a unique index color into an off screen framebuffer. Then by looking at what values can be found therein you know which faces are present in a given area.
Later I need to remesh
This is called topology modification and is completely outside the scope of OpenGL.
that selected area and map an image over it which I know
You can use a image based approach for this again, however you must know in which way you want to make images to faces first. If you want to unwrap the mesh, then OpenGL is of no help. However if you want the user to be able to "directly draw" onto the mesh, this can be done by drawing texture coordinates into another off screen framebuffer and by this reverse mapping screen coordinates to texture coordinates.
I recently started looking at cocos2d game development.
What's the difference between sprite and texture?
Maybe I could through in 'bitmap' in there. What is a bitmap?
They all seem to be the same thing as 2d image.
A texture is an in-memory image that the device can draw onto the screen.
A sprite actually draws the texture, or just a specific rectangle of the texture, on the screen. The sprite can be scaled, rotated, positioned, skewed, tinted (colorized) among other things.
Multiple sprites can share the same texture. The texture is only loaded to memory once regardless of how many sprites are using the same texture. Moreover with CCSpriteBatchNode you can "batch" the drawing of all sprites that are using the same texture to achieve better performance.
A bitmap is a general term for a computer image where each pixel is represented by one or more bits. There's also the image format BMP which is/was popular on Windows. Most people would just say "image" these days as there are other forms of "bitmaps" that are not images. For example in AI code you often have bitmaps (arrays of bits) that represent state information of the AI or pathfinding algorithms for all areas of the game world. Ie each area in the world could have a "blocking" bit, or a "resource" bit that helps the AI making decisions.
See also Wikipedia:
Texture Mapping
Bitmap
you can load texture into memory, for example your file with image is texture. sprite is object with set of parameters, several of them are pointer to the texture, size and texture coordinate.
you can load texture 2048x2048 into memory, then create sprite with part of this texture.
Any good references on displaying sequence of images from a video as voxel data in OpenGL? I want to display all these images at once as a cuboid with 50% alpha and navigate using keyboard or mouse.
Check out this tutorial on setting up a 3D texture.
If you then render slices through the texture array with the appropriate UVW coordinates you will get what you are after.