I need to write a shader of pressure map. Similar to the following:
Card
It is necessary to provide closed lines with borders, which shows tonality of pressure and the corresponding color gradation areas with different pressures. Maybe in future it will need to remake in 3D... Shader Language is Cg...
I have no idea where to start. I would be grateful for any advice!
What does your input data look like? Is it a texture with a pressure value at each texel? If so the coloured gradation areas should be fairly simple to achieve. Just have a look-up texture that maps pressure to colour and look up your colour in it using the pressure value at the current pixel as the UV.
Smooth, equal width contour lines are slightly trickier. You could just put black in your look-up texture at contour values but you'll get contour lines of varying width and broken lines in regions where the pressure is changing rapidly. You should be able to get fairly clean lines by using the partial derivatives from your pressure texture though, something like the technique described in this forum thread.
Related
I am trying my hand at writing a 3d graphics engine, but I am having some trouble with drawing the shapes in the correct order.
When I translate the points of triangles into window space, i.e. the 2-dimensional space that directly correlates to position on the screen, in addition to an x and y position of each point, I also assign them a depth variable that stores how far away from the viewer that point was in 3d space.
At the moment, the only shapes I am rendering are triangles. My current render order algorithm sorts the triangles by the average depth of their 3 points. I knew when I started it that it would not be perfect, but I wanted a placeholder for testing.
For testing purposes, I constructed a square box with an open top, each side being a different color and made from 2 triangles, as shown below:
As you can see from the image above, the algorithm I am using works most of the time. However, at certain angles and positions, the triangles will be rendered in the wrong order, as show below:
As you can see, one of the cyan triangles on the bottom of the box is being drawn before one of the yellow triangles on the side. Clearly, sorting the triangles by the average depth of their points is not satisfactory.
Is there a better method of ordering shapes so that they are rendered in the correct order?
The standard method to draw 3D in correct depth order is to use a Z-buffer.
Basically, the idea is that for each pixel you set in the color buffer, you also set it's interpolated depth in the z (depth..) buffer. Whenever you're about to paint the next pixel, you first check that z-buffer to validate the new pixel if in front of the already painted pixel.
On top of that you can add various sorts of optimizations, such as sorting triangles in order to minimize the number of times you actually paint the color buffer.
On the other hand, it's sometimes required to do the exact opposite in order to properly handle transparency or other "advanced" effects.
I'm looking for an efficient way to display lots of spheres using directx 11. The spheres are defined by (x,y,z,r) where (x,y,z) are coordinates in space and r is the radius. I want to display only the spheres that can be seen, meaning that spheres that are not in the field of view and spheres that are too small to be seen wouldn't be drawn. However, if a group of spheres smaller than one pixel is at least as big as one pixel, then I want to display the most predominant color. Spheres have only one color and different levels of transparency. Any help would be appreciated and incomplete answers are acceptable.
You need several things. First an indexed unit sphere geometry, second a buffer to store the sphere instance properties ( position, radius and color ) and third a small buffer for the API parameters yet to come. The three combines in a single 'ID3D11DeviceContext::DrawIndexedInstancedIndirect'
The remaining question is "how to feed the instance buffer ?". cpu is easy, just apply frustum culling, sort back to front because of the transparency and apply a merge based on the screen projection, update the buffer and use 'ID3D11DeviceContext::DrawIndexedInstanced'.
gpu version will do the same thing with compute shaders but will be harder to implement. The advantage, zero cpu/gpu synchronization and should support far more instance.
Background
Using gluTess to build a triangle list in Direct3D9 from a GDI+ DrawString(..) path:
A pixel shader (v3.0) is then used to fill in the shape. When painting with opaque values, everything looks fine:
The problem
At certain font sizes, if the color has an alpha component (ie Argb #55FFFFFF) we begin to see these nasty tessellation artifacts where triangles may overlap ever so slightly:
At larger font sizes the problem is sometimes not present:
Using Intel's excellent GPA Frame Analyzer Pixel History tool, we can see in areas where the artifacts occur, the pixel has been "touched" 3 times from the single Erg.
I'm trying to figure out how I can stop my pixel shader from touching the same pixel more than once.
Other solutions relating to overdraw prevention seem to be all about zbuffer strategies, however this problem is more to do with painting of a single 2D triangle list within a single pixel shader pass.
I'm at a bit of a loss trying to come up with a solution on this one. I was hoping that HLSL might have some sort of "touch each pixel only once" flag, but I've been unable to find anything like that. The closest I've found was to set the BLENDOP to MAX instead of ADD. But the output is not correct when blending over other colors in the scene.
I also have SRCBLEND = ONE, DSTBLEND = INVSRCALPHA. The only combination of flags which produce correct output (albeit with overdraw artifacts.)
I have played with SEPARATEALPHABLENDENABLE in the GPA frame analyzer, which sounded like almost exactly what I need here -- set blending to MAX but only on the "alpha" channel, however from what I can determine, that setting (and corresponding BLENDOPALPHA) affects nothing at all.
One final thing I thought of was to bake text as opaque onto a texture, and then repaint that texture into the scene with the appropriate alpha value applied, however this doesn't actually work in this project because I also support gradient brushes, where stop values may contain alpha, meaning either the artifacts would still be seen, or the final output just plain wrong if we stripped the alpha away from the stop values prior to baking to a texture. Also the whole endeavor would be hideously expensive.
Any hints or pointers would be appreciated. Thanks for reading.
The problem you're seeing shouldn't happen.
If two of your triangles are overlapping it's because you've placed the vertices in such a way that when the adjacent triangles are drawn, they overlap. What's probably happening is that these two adjacent triangles share two vertices, but each triangle has its own copy of each vertex that's been calculated to be in a very, very slightly different position.
The solution to the problem isn't to try and make the pixel shader touch the pixel only once it's to use an index buffer (if you aren't already) and have the shared vertices between each triangle actually share the same vertex and not use one that's ever-so-slightly not in the same place as the one used by the adjacent triangle.
If you aren't in control of the tessellation algorithm being used you may have to run a pass over the vertex buffer after its been generated to detect and merge vertices that are within some very small tolerance of one another. Even without an index buffer, a naive solution would be this:
For each vertex in the vertex buffer, compare its position to every other vertex in the rest of the vertex buffer.
If two vertices are within some small tolerance of another, replace the second vertex's position with the position of the one you are comparing it against.
This should have the effect of pairing up the positions of two vertices if they are close enough that you deem them to be the same.
You now shouldn't have any problem with overlapping triangles. In everyday rendering two triangles share edges with each other all the time and you won't ever get the effect where they appear to every-so-slightly overlap. The hardware guarantees that a sample point is either on one side of the line or the other, but never both at the same time, no matter how close the point is to the line (even if it's mathematically on the line, it still fails on one side or the other).
I'm using DirectX10 to simulate a water surface, and I'm now with a height map,which is a 2D array of the heights(y) at the points (x,z). But to draw it on the screen, I must turn it into a mesh or have a index to draw triangle topology.
But the data is too large to do it manually. Are there any methods for me to draw it on the screen. I hope it's easy to implement. If there is function included in DirectX10 which can make it, the it's the best one for me.
Create a mesh that format a grid of squares (each made of two triangles) and set all vertices y = 0. In the vertex shader sample the heightmap and add the value stored in the heightmap to the y of the vertice.
This might help you.
P.S: If the area you want it to cover is too big you should take a look at terrain LOD techniques (should work the same for water).
I'm sure you can make a mesh out of it. I doubt you can generate the heightmap for a water surface that is too large to "meshify".
Why are you looking at Diamond square. For a 512x512 heightmap all you need to do is define a set of point and then generate the triangles for it. Its really very simple.
I'm learning XNA by doing and, as the title states, I'm trying to see if there's a way to fill a 2D area that is defined by a collection of vertices on a plane. I want to fill with a color, not a file-based texture.
For an example, take a rounded rectangle whose vertices are defined by four quarter-circle triangle fans. The vertices are defined by building a collection of triangles, but the triangles may not be adjacent.
Additionally, I would like to fill it with more than a single color -- i.e. divide the bound area into four vertical bands and have each a different color. You don't have to provide me the code, pointing me towards resources will help a great deal. I can be handy with Google (which I did try first, but have failed miserably).
This is as much an exploration into "what's appropriate for XNA" as it is the implementation of it. Being pretty new to XNA, I'm wanting to also learn what should and shouldn't be done on top of what can and can't be done.
Not too much but here's a start:
The color fill is accomplished by using a shader. Reimer's XNA Tutorials on pixel shaders is a great resource on the topic.
You need to calculate the geometry and build up vertex buffers to hold it. Note that all vector geometry in XNA is in 3D, but using a camera fixed to a plane will simulate 2D.
To add different colors to different triangles you basically need to group geometry into separate vertex buffers. Then, using a shader with a color parameter, for each buffer,
set the appropriate color before passing the buffer to the graphics device. Alternatively, you can use a vertex format containing color information, which basically let you assign a color to each vertex.