Coin3D uses single-sided rendering by default like the image below：
(source: gitee.com)
How does open inventor / coin3d enable two-sided rendering like OpenGL？
SoShapeHints is the answer, but this summary may be clearer:
Two-sided lighting and backface culling are disabled by default.
Two-sided lighting: enabled if not solid and ordered vertices.
Set vertexOrdering to COUNTERCLOCKWISE (usually) or CLOCKWISE.
Backface culling: enabled if solid and ordered vertices.
Set shapeType to SOLID.
You should add a SoShapeHints node before the geometry in the scenegraph either with shapeType set to UNKNOWN_SHAPE_TYPE if you already set the vertexOrdering to CLOCKWISE or COUNTERCLOCKWISE, or with the vertexOrdering set to UNKNOWN_ORDERING for any shape type, e.g.
ShapeHints {
vertexOrdering UNKNOWN_ORDERING
shapeType UNKNOWN_SHAPE_TYPE
}
For further explanation see the SoShapeHints documentation of Coin3D
Related
How do I style the transform anchors (e.g., blue boxes) on a transformable Konva element? Note I'm using Konva with konva-react.
Example 1:
In other words, what if I wanted to make the boxes grey, and semi-transparent? Or change the size?
Example 2:
Or, what if I waned to remove the anchors and make the entire edge of a Rect able to be grabbed to resize? In other words, make the anchor transparent and full-height/full-width.
I’d start your research using the elements from this example:
https://konvajs.org/docs/sandbox/Image_Resize.html
It shows that the transformer has various bits you can style in your own way. Good luck with that.
I am currently working on an algorithm to detect the playing area of a pool table. For this purpose, I captured an image, transformed it to grayscale, and used a Sobel operator on it. Now I want to detect the playing area as a box with 4 corners located in the 4 corners of the table.
Detecting the edges of the table is quite straightforward, however, it turns out that detecting the 4 corners is not so easy, as there are pockets in the pool table. Now I just want to fit a line to each of the side edges, and from those lines, I can compute the intersects, which are the corners for my table.
I am stuck here, because I could not yet come up with a good solution to find these lines in my image. I can see it very easily when I used the Sobel operator. But what would be a good way of detecting it and computing the position of the corners?
EDIT: I added some sample Images
Basic Image:
Grayscale Image
Sobel Filter (horizontal only)
For a general solution, there will be many sources of noise: problems with cloth around the rails, wood texture (or no texture) on the rails, varying lighting, shadows, stains on the cloth, chalk on the rails, and so on.
When color and lighting aren't dependable, and when you want to find the edges of geometric objects, then it's best to think in terms of edge pixels rather than gray/color pixels.
A while back I was thinking of making a phone-based app to save ball positions for later review, including online, so I've though a bit about this problem. Although I can provide some guidance for your current question, it occurs to me you'll run into new problems each step of the way, so I'll try to provide a more complete answer.
Convert the image to grayscale. If we can't get an algorithm to work in grayscale, we'll inevitably run into problems with color. (See below)
[TBD] Do some preprocessing to reduce noise.
Find edge points using Sobel or (if you must) Canny.
Run Hough lines detection, but with a few caveats and parameterizations as described below.
Find the lines described a keystone-shaped quadrilateral. (This will likely be the inner quadrilateral of two: one inside the rail on the bed, and the other slightly larger quadrilateral at the cloth/wood rail edge at top.)
(Optional) Use the side pockets to help determine the orientation of the quadrilateral.
Use an affine transform to map the perspective-distorted table bed to a rectangle of [thankfully] known relative dimensions. We know the bed sizes in advance, so you can remap the distorted rectangle to a proper rectangle. (We'll ignore some optical effects for now.)
Remap the color image to the perspective-corrected rectangle. You'll probably need to tweak the positions of some balls.
General notes:
Filtering by color in the general sense can be difficult. It's tempting to think of the cloth as being simply green, blue, or red (or some other color), but when you look at the actual RGB values and try to separate colors you'll begin to appreciate what a nightmare working in color can be.
Optical distortion might throw off some edges.
The far short rail may be difficult to detect, BUT you do this: find the inside lines for the two long rails, then search vertically between the two rails for the first strong horizontal-ish edge at the far side of the image. That'll be the far short rail.
Although you probably want to use your phone camera for convenience, using a Kinect camera or similar (preferably smaller) device would make the problem easier. Not only would you have both color data and 3D data, but you would eliminate some problems with lighting since the depth data wouldn't depend on visible lighting.
For your app, consider limiting the search region for rail edges to a perspective-distorted rectangle. The user might be able to adjust the search region. This could greatly simplify the processing, and could help you work around problems if the table isn't lit well (as can be the case).
If color segmentation (as suggested by #Dima) works, get the outline of the blob using contour following. Then simplify the outline to a quadrilateral (or a polygon of few sides) by the Douglas-Peucker algorithm. You should find the four table edges this way.
For more accuracy, you can refine the edge location by local search of transitions across it and perform line fitting. Then intersect the lines to get the corners.
The following answer assumes you have already found the positions of the lines in the image. This however can be done "easily" by directly looking at the pixels and seeing if they are in a "line". Usually it is easier to detect this if the image has been deskewed first as well, i.e. Rotated so the rectangle (pool table) is more like this: [] than like /=/. Then it is just a case of scanning the pixels and if there are ones of similar colour alongside it assuming a line is between them.
The code works by looping over the lines found in the image. Whenever the end points of each line falls within a tolerance on within the x and y coordinates it is marked as a corner. Once the corners are found I take the average value between them to find where the corner lies. For example:
A horizontal line ending at 10, 10 and a vertical line starting at 12, 12 will be found to be a corner if there is a tolerance of 2 or more. The corner found will be at: 11, 11
NOTE: This is just to find Top Left corners but can easily be adapted to find all of them. The reason it has been done like this is because in the application where I use it, it is faster to sort each array first into an order where relevant values will be found first, see: Why is processing a sorted array faster than an unsorted array?.
Also note that my code finds the first corner for each line which might not be applicable for you, this is mainly for performance reasons. However the code can easily be adapted to find all the corners with all the lines then either select the "more likely" corner or average through them all.
Also note my answer is written in C#.
private IEnumerable<Point> FindTopLeftCorners(IEnumerable<Line> horizontalLines, IEnumerable<Line> verticalLines)
{
List<Point> TopLeftCorners = new List<Point>();
Line[] laHorizontalLines = horizontalLines.OrderBy(l => l.StartPoint.X).ThenBy(l => l.StartPoint.Y).ToArray();
Line[] laVerticalLines = verticalLines.OrderBy(l => l.StartPoint.X).ThenBy(l => l.StartPoint.Y).ToArray();
foreach (Line verticalLine in laVerticalLines)
{
foreach (Line horizontalLine in laHorizontalLines)
{
if (verticalLine.StartPoint.X <= (horizontalLine.StartPoint.X + _nCornerTolerance) && verticalLine.StartPoint.X >= (horizontalLine.StartPoint.X - _nCornerTolerance))
{
if (horizontalLine.StartPoint.Y <= (verticalLine.StartPoint.Y + _nCornerTolerance) && horizontalLine.StartPoint.Y >= (verticalLine.StartPoint.Y - _nCornerTolerance))
{
int nX = (verticalLine.StartPoint.X + horizontalLine.StartPoint.X) / 2;
int nY = (verticalLine.StartPoint.Y + horizontalLine.StartPoint.Y) / 2;
TopLeftCorners.Add(new Point(nX, nY));
break;
}
}
}
}
return TopLeftCorners;
}
Where Line is the following class:
public class Line
{
public Point StartPoint { get; private set; }
public Point EndPoint { get; private set; }
public Line(Point startPoint, Point endPoint)
{
this.StartPoint = startPoint;
this.EndPoint = endPoint;
}
}
And _nCornerTolerance is an int of a configurable amount.
A playing area of a pool table typically has a distinctive color, like green or blue. I would try a color-based segmentation approach first. The Color Thresholder app in MATLAB gives you an easy way to try different color spaces and thresholds.
I've created a simple DirectX app that renders a field of vertices. Vertices are rendered like this (if viewed from top):
|\|\|\|\|
|\|\|\|\|
Each triangle is rendered like this:
1
|\
2 3
Which should mean that the polygon is counterclockwise and not be rendered, but it is. Anyway when viewed from top the plane is perfect.
However, when viewed from another level some polygons are sort of transparent and you can see geometry behind them. I've highlighted some of the place where this is happening.
I am thinking this is some of the basic, beginner problems. What am I missing? My rasterizer description is such:
new RasterizerStateDescription
{
CullMode = CullMode.Front,
IsAntialiasedLineEnabled = true,
IsMultisampleEnabled = true,
IsDepthClipEnabled = true,
IsFrontCounterclockwise = false,
IsScissorEnabled = true,
DepthBias = 1,
DepthBiasClamp = 1000.0f,
FillMode = FillMode.Wireframe,
SlopeScaledDepthBias = 1.0f
};
This is by design. FillMode.Wireframe only draws edges of each triangle as lines. That's all.
Do a first pass with a solid fill mode and depth writes on and a color mask (RenderTargetWriteMask in D3D11 terminology), and a second one with depth test on (but depth writes off) and wireframe mode on. You will probably need depth bias too since lines and triangles are not rasterized the same way (and their z can differ at equal fragment position).
BTW, this technique is known as hidden line removal. You can check this presentation for more details.
Turned out I just had no depth-stencil buffer set up. Oh well.
I've noticed that the OpenVG transformation matrix is ignored by the text rendering routine at all and I cannot control the text position with it manually with VG_GLYPH_ORIGIN parameter.
I'm implementing a scene graph. I found out that I can use vgGetMatrix, read components 6 and 7 of the current 3x3 transform matrix and set VG_GLYPH_ORIGIN to those values before drawing a block of text. This allows the text origin to be placed in correct place, but the text is still always displayed left-to-right.
However, this itself doesn't enable me to do any other transformations, like rotation. I'm surprised because the text is composed from VGPaths and they are indeed transformed
Is there a way to make the text rotated with OpenVG 1.1? Or should I ignore the text functionality from OpenVG 1.1 and draw the letters as individual paths or images manually?
All the draw functions use a different user->surface matrix:
vgDrawPath uses VG_MATRIX_PATH_USER_TO_SURFACE
vgDrawImage uses VG_MATRIX_IMAGE_USER_TO_SURFACE
vgDrawGlyph/vgDrawGlyphs use VG_MATRIX_GLYPH_USER_TO_SURFACE
By default, all of the matrix functions (vgTranslate, vgRotate, vgLoadMatrix, etc) operate on VG_MATRIX_PATH_USER_TO_SURFACE. To change the active matrix, call vgSeti with VG_MATRIX_MODE as the first argument:
vgSeti(VG_MATRIX_MODE, VG_MATRIX_GLYPH_USER_TO_SURFACE);
/* now vgTranslate, vgRotate, etc will operate on VG_MATRIX_GLYPH_USER_TO_SURFACE */
I have a tex2D sampler I want to only return precisely those colours that are present on my texture. I am using Shader Model 3, so cannot use load.
In the event of a texel overlapping multiple colours, I want it to pick one and have the whole texel be that colour.
I think to do this I want to disable mipmapping, or at least trilinear filtering of mips.
sampler2D gColourmapSampler : register(s0) = sampler_state {
Texture = <gColourmapTexture>; //Defined above
MinFilter = None; //Controls sampling. None, Linear, or Point.
MagFilter = None; //Controls sampling. None, Linear, or Point.
MipFilter = None; //Controls how the mips are generated. None, Linear, or Point.
//...
};
My problem is I don't really understand Min/Mag/Mip filtering, so am not sure what combination I need to set these in, or if this is even what I am after.
What a portion of my source texture looks like;
Screenshot of what the relevant area looks like after the full texture is mapped to my sphere;
The anti-aliasing/blending/filtering artefacts are clearly visible; I don't want these.
MSDN has this to say;
D3DSAMP_MAGFILTER: Magnification filter of type D3DTEXTUREFILTERTYPE
D3DSAMP_MINFILTER: Minification filter of type D3DTEXTUREFILTERTYPE.
D3DSAMP_MIPFILTER: Mipmap filter to use during minification. See D3DTEXTUREFILTERTYPE.
D3DTEXF_NONE: When used with D3DSAMP_MIPFILTER, disables mipmapping.
Another good link on understanding hlsl intrinsics.
RESOLVED
Not an HLSL issue at all! Sorry all. I seem to ask a lot of questions that are impossible to answer. Ogre was over-riding the above settings. This was fixed with;
Ogre::MaterialManager::getSingleton().setDefaultTextureFiltering(Ogre::FO_NONE , Ogre::FO_NONE, Ogre::FO_NONE);
What it looks to me is that you're getting the values from a lower level mip-map (unfiltered) than the highest detail you're showing.
MipFilter = None
should prevent that, unless something in the code overrides it. So look for calls to SetSamplerState.
What you have done should turn off filtering. There are 2 potential issues, that I can think of, though
1) The driver just ignores you and filters anyway (If this is happening there is nothing you can do)
2) You have some form of edge anti-aliasing enabled.
Looking at your resulting image that doesn't look much like bilinear filtering to me so I'd think you are suffering from having antialiasing turned on somewhere. Have you set the antialiasing flag when you create the device/render-texture?
If you want to have really just one texel, use load instead of sample. load takes (as far as i know) an int2as an argument, that specifies the actual array coordinates in the texture. load looks then up the entry in your texture at the given array coordinates.
So, just scale your float2, e.g. by using ceil(float2(texCoord.x*textureWidth, texCoord.y*textureHeight)).
MSDN for load: http://msdn.microsoft.com/en-us/library/bb509694(VS.85).aspx
When using just shader model 3, you could a little hack to achieve this: Again, let's assume that you know textureWidth and textureHeight.
// compute floating point stride for texture
float step_x = 1./textureWidth;
float step_y = 1./textureHeight;
// compute texel array coordinates
int target_x = texCoord.x * textureWidth;
int target_y = texCoord.y * textureHeight;
// round to values, such that they're multiples of step_x and step_y
float2 texCoordNew;
texCoordNew.x = target_x * step_x;
texCoordNew.y = target_y * step_y;
I did not test it, but I think it could work.