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• Multiplication for MVP matrices: Any benefits to doing so within the vertex shader?

  - by Nick Wiggill

  I'd like to understand under what circumstances (if any) it is worth doing MVP matrix multiplication inside a vertex shader. The vertex shader is run once per vertex, and a single mesh typically contains many vertices. All MVP inputs remain the same for each vertex in the vertex batch relating to a given draw call (model). Surely then, you're always better off keeping the multiplications in the client code, such that you pass in the whole MVP precalculated as a uniform? (avoiding redundant ops between individual vertices)

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• OpenGL/GLSL checking if shader compiled fine on intel cards

  - by clamp

  hello, i am using this code to check if my glsl shader compiled fine. glGetObjectParameterivARB(obj, GL_OBJECT_INFO_LOG_LENGTH_ARB, &infologLength); if (infologLength > 1) { int charsWritten = 0; char * const infoLog = new char[infologLength]; glGetInfoLogARB(obj, infologLength, &charsWritten, infoLog); tError(infoLog, false); delete infoLog; } } the length of the returned string is empty on nvidia and ATI cards, but on intel cards this one returns the string "no errors." now what is the best way to find out, if there are really no errors? should i just check for this string? or is there a convention what this function glGetInfoLogARB should return?

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• Help with Pixel Shader effect for brightness and contrast

  - by Hans

  What is a simple pixel shader script effect to apply brightness and contrast? I found this one, but it doesn't seem to be correct: sampler2D input : register(s0); float brightness : register(c0); float contrast : register(c1); float4 main(float2 uv : TEXCOORD) : COLOR { float4 color = tex2D(input, uv); float4 result = color; result = color + brightness; result = result * (1.0+contrast)/1.0; return result; } thanks!

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• Applying a pixel shader effect to a portion of an image

  - by Nick

  I have a ScrollViewer that contains a very large video (16 megapixel @ 10fps) and I want to apply a pixel shader effect to it. Given the size of the images I can't apply the effect directly to the image. So I apply the effect to the ScrollContentPresenter in the control style. Which is great, everything runs nice and fast. However, I'm also rendering annotations inside of the ScrollContentPresenter which I do NOT want effects applied to (but they need to move and scale along with the image). Is there to apply the effect just to the clipped and displayed portion of the image or do I need to build a rather more complex control?

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• How to do geometric projection shadows?

  - by John Murdoch

  I have decided that since my game world is mostly flat I don't need better shadows than geometric projections - at least for now. The only problem is I don't even know how to do those properly - that is to produce a 4x4 matrix which would render shadows for my objects (that is, I guess, project them on a horizontal XZ plane). I would like a light source at infinity (e.g., the sun at some point in the sky) and thus parallel projection. My current code does something that looks almost right for small flying objects, but actually is a very rude approximation, as it doesn't project the objects onto the ground, but simply moves them there (I think). Also it always wrongly assumes the sun is always on the zenith (projecting straight down). Gdx.gl20.glEnable(GL10.GL_BLEND); Gdx.gl20.glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA); //shells shellTexture.bind(); shader.begin(); for (ShellState state : shellStates.values()) { transform.set(camera.combined); transform.mul(state.transform); shader.setUniformMatrix("u_worldView", transform); shader.setUniformi("u_texture", 0); shellMesh.render(shader, GL10.GL_TRIANGLES); } shader.end(); // shadows shader.begin(); for (ShellState state : shellStates.values()) { transform.set(camera.combined); m4.set(state.transform); state.transform.getTranslation(v3); m4.translate(0, -v3.y + 0.5f, 0); // TODO HACK: + 0.5f is a hack to ensure the shadow appears above the ground; this is overall a hack as we are just moving the shell to the surface instead of projecting it on the surface! transform.mul(m4); shader.setUniformMatrix("u_worldView", transform); shader.setUniformi("u_texture", 0); // TODO: make shadow black somehow shellMesh.render(shader, GL10.GL_TRIANGLES); } shader.end(); Gdx.gl.glDisable(GL10.GL_BLEND); So my questions are: a) What is the proper way to produce a Matrix4 to pass to openGL which would render the shadows for my objects? b) I am supposed to use another fragment shader for the shadows which would paint them in semi-transparent grey, correct? c) The limitation of this simplistic approach is that whenever there is some object on the ground (it is not flat) the shadows will not be drawn, correct? d) Do I need to add something very small to the y (up) coordinate to avoid z-fighting with ground textures? Or is the fact they will be semi-transparent enough to resolve that problem?

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• Value object or not for 3d points ?

  - by Stefano Borini

  I need to develop a geometry library in python, describing points, lines and planes in 3d space, and various geometry operations. Related to my previous question. The main issue in the design is if these entities should have identity or not. I was wondering if there's a similar library out there (developed in another language) to take inspiration from, what is the chosen design, and in particular the reason for one choice vs. the other.

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• GLSL: How to get pixel x,y,z world position?

  - by Rookie

  I want to adjust the colors depending on which xyz position they are in the world. I tried this in my fragment shader: vec4 pos = vec4(gl_FragCoord); // get pixel position but it seems that the z-coord is always towards my camera... how do i make the coords independent from my camera position/angle? Edit: if it matters, heres my vertex shader: gl_Position = ftransform(); Edit2: changed title, so i want world coords, not screen coords!

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• Need guidelines for optimizing WebGL performance by minimizing shader changes

  - by brainjam

  I'm trying to get an idea of the practicality of WebGL for rendering large architectural interior scenes, consisting of 100K's of triangles. These triangles are distributed over many objects, and there are many materials in the scene. On the other hand, there are no moving parts. And the materials tend to be fairly simple, mostly based on texture maps. There is a lot of texture map sharing .. for example all the chairs in scene will share a common map. There is also some multitexturing - up to three textures overlaid in a material. I've been doing a little experimentation and reading, and gather that frequently switching materials during a rendering pass will slow things down. For example, a scene with 200K triangles will have significant performance differences, depending on whether there are 10 or 1000 objects, assuming that each time an object is displayed a new material is set up. So it seems that if performance is important the scene should be sorted by materials so as to minimize material switching. What I'm looking for is guidelines on how to think of the overhead of various state changes, and where do I get the biggest bang for the buck. For example, what are the relative performance costs of, say, gl.useProgram(), gl.uniformMatrix4fv(), gl.drawElements() should I try to write ubershaders to minimize shader switching? should I try to aggregate geometry to minimize the number of gl.drawElements() calls I realize that mileage may vary depending on browser, OS, and graphics hardware. And I'm also not looking for heroic measures. Just some guidelines from people who have already had some experience in making scenes fast. I'll add that while I've had some experience with fixed-pipeline OpenGL programming in the past, I'm rather new to the WebGL/OpenGL ES 2.0 way of doing things.

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• Creating SVG map from geometry stored in MySQL

  - by Barnabe

  I have a group of geometries stored in MySQl (as polygon and as well-known text) representing counties. I can build a table of geometries and color codes after querying some county data (say GDP per capita). What is the best way to export this as an SVG map? I cannot find any reference to SVG conversion in the MySQL documentation.

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• opengl shader make color "disappear"

  - by JFoulkes

  hi, I'm new to opengl and shaders. I'm trying to do some augmented reality on the iphone and messing about with shaders to alter a feed from the camera. What I'm trying to achieve is the appearance that an object in a picture has disappeared by setting the color to match the surrounding colour. I have a yellow rectangle and in it is a small red circle. I want to give the impressed the red circle has disappeared by setting the colour to be yellow. It won't always be solid colours but I'm just trying to get the basics down first. Currently I have a simple shader which will make a red colour lighter but this isn't ideal because it doesn't get close to the surrounding colour and I want this to work for different coloured objects and different coloured surrounding. I'm not even 100% shaders are what I need to be looking at or even opengl. I'm using it because of the performance it gives on the iPhone. I'm basically asking if: Anyone has done or seen anything similar Am I barking up the wrong tree using opengl es and opengl sl? Is this even possible? Cheers.

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• Code to extrude 2d geometry to 3d

  - by Bgnt44

  Hi, is there any simple way to extrude a 2d geomtry (vectors ) to a 3d shape assuming extruding parameter are lenght (double) and angle (degree) so it should render like a cone ( all z lines going to one point )

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• Create Linework/Geometry Using Text Style in AutoCAD

  - by Kratz

  I'm working in AutoCAD using the ObjectARX .Net API. Is there a way to either create text using lines/curves/polylines, or explode an existing text object into lines/ect? Prefereable I would like to be able to generate linework based on an exsiting AutoCAD text style. Edit: I was able to find the source for the TxtExp command here . However its in AutoCADs own Lisp language, and I can't make heads or tails of it.

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• What library should I use for 2D Geometry? [closed]

  - by Luka

  I've been working on a 2D game in java, but found that java just didn't cut it for me and had forced me to a lot of bad design choices, so I've decided to port all my work to c++. The main reason I've decided change to c++ is that i had reached a point where i had 3 geometry libraries (the native, one from the game engine and one to handle "complex" polygons), none of witch worked very well together and i couldn't keep track of them. I'm new to c++, but i know all the basics. My question is, what would be a good geometry library to use, ideally it should be able to handle integer and decimal data types, have point, line, and polygon classes witch are able to check for intersection and contains. Thanks in advance, Luka

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• iPad GLSL. From within a fragment shader how do I get the surface - not vertex - normal

  - by dugla

  Is it possible to access the surface normal - the normal associated with the plane of a fragment - from within a fragment shader? Or perhaps this can be done in the vertex shader? Is all knowledge of the associated geometry lost when we go down the shader pipeline or is there some clever way of recovering that information in either the vertex of fragment shader? Thanks in advance. Cheers, Doug twitter: @dugla

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• Intersections of 3D polygons in python

  - by Andrew Walker

  Are there any open source tools or libraries (ideally in python) that are available for performing lots of intersections with 3D geometry read from an ESRI shapefile? Most of the tests will be simple line segments vs polygons. I've looked into OGR 1.7.1 / GEOS 3.2.0, and whilst it loads the data correctly, the resulting intersections aren't correct, and most of the other tools available seem to build on this work. Whilst CGAL would have been an alternative, it's license isn't suitable. The Boost generic geometry library looks fantastic, but the api is huge, and doesn't seem to support wkt or wkb readers out of the box.

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• Collision detection, alternatives to "push out"

  - by LaZe

  I'm moving a character (ellipsoid) around in my physics engine. The movement must be constrained by the static geometry, but should slide on the edges, so it won't be stuck. My current approach is to move it a little and then push it back out of the geometry. It seems to work, but I think it's mostly because of luck. I fear there must be some corner cases where this method will go haywire. For example a sharp corner where two walls keeps pushing the character into each other. How would a "state of the art" game engine solve this?

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• Mixing a4 and a3 in one Latex file

  - by jorgusch

  Hello, I am finishing my thesis and have a large appendix. Some tables only look good, if first done on a3 and then (paper)printed on a4. Anyhow, working all the files seperalty is fine, but I struggle to compile all in one. I use the geometry package and start the document with: \usepackage[a4paper,left=30mm,right=20mm,top=20mm, bottom=20mm]{geometry} For the appendix, I want to include the table and use \newgeometry{a3paper,left=25mm,right=15mm, top=15mm, bottom=15mm} However, the command is completely ignored and I can read "a3paper,left=25mm,right=15mm, top=15mm, bottom=15mm" above the table. What did I miss? Is it even possible? If not, how do I get the numbers right, if I have to include it as a pdf (which works)? Thanks!

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• How to get a flat, non-interpolated color when using vertex shaders.

  - by Brett

  Hi, Is there a way to achieve this? If I draw lines like this glShadeModel(GL_FLAT); glBegin(GL_LINES); glColor3f(1.0, 1.0, 0.0); glVertex3fv(bottomLeft); glVertex3fv(topRight); glColor3f(1.0, 0.0, 0.0); glVertex3fv(topRight); glVertex3fv(topLeft); . . (draw a square) . . glEnd(); I get the desired result (a different colour for each edge) but I want to be able to calculate the fragment values in a shader. If I do the same after setting up my shader program I always get interpolated colors between vertices. Is there a way around this? (would be even better if I could get the same results using quads) Thanks

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• WebGL transparent black.

  - by Catalin Dumitru

  I have a strange problem that I can't figure out when trying to do blending in WebGL. Black is rendered fully transparent , and everything with shades of grey in it is rendered also semi transparent. I have set it to use the alpha channel as the source for transparency, and in some respect it works, every thing that isn't black/grey is rendered differently when changing the alpha value. but even when I set the alpha to 1, black is still displayed transparent. This is how I enable transparency: this.gl.blendFunc(this.gl.SRC_ALPHA, this.gl.ONE); this.gl.enable(this.gl.BLEND); this.gl.disable(this.gl.DEPTH_TEST); And the part of the shader that does transparency: gl_FragColor = vec4(texColor.rgb * vLightWeight, texColor.a * uAlpha); where texColor is the texture color that is being sampled, vLightWeight is the shadowing that is being calculated in the vertex shader, and uAlpha the uniform which I use for transparency.

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• Number range for color in GLSL

  - by kotoko

  I'm figuring out how to set a colour in a Fragment Shader. This statement gl_FragColor = (0.1,0.6,1,1); gives me white regardless of what I enter in the first 3 values. I was expecting to either give it values between 0 and 255 or 0 and 1 but neither seems to work. I can change how bright it is with values from 0 to 1 in the fourth value, but nothing for colour. Can anybody tell me if: gl_FragColor is the right variable to set. What is the range of values for the first three values. What am I currently making the Shader do.

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• How to code a 4x shader/filter which emulates arcade crt display behavior?

  - by Arthur Wulf White

  I want to write a shader/filer probably in adobe Pixel Bender that will do the best job possible in emulating the fill of an oldskul monochromatic arcade CRT screen. Much like this here: http://filthypants.blogspot.com/2012/07/customizing-cgwgs-crt-pixel-shader.html Here are some attributes I know will exist in this filter: It will take in a low res image 160 x 120 and return a medium res image 640 x 480. It will add scanlines It will blur the color channels to create that color bleeding effect It will distort the shape of the image from a perfect rectangle into a rounder shape. The question is, could you please provide any other attributes that are beneficial to emulating an arcade CRT feel and links and resources on coding these effects. Thanks

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• GLSL Shader Effects: How to do motion blur, etc?

  - by DevilWithin

  I am not sure how right it is to ask this question, but still here it goes. I have a full 2D environment, with sprites going around as landscape, characters, etc And to make it more state-of-art looking, i want to implement a motion blur effect, similar to modern FPS's (i.e. crysis) blur when moving fast the camera. In a sidescroller, the desired effect is having this slight blur appearing to give the idea of fast movement, when the camera is moving. If anyone could give me some tips on doing this, im assuming in a pixel shader, i'd be grate. Also, if anyone has other good tips on cool pixel shader effects for 2D games it would be awesome, like some stylizing post fx, such as previous Prince of Persia illustrative style. Thanks

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• What causes player box/world geometry glitches in old games?

  - by Alexander

  I'm looking to understand and find the terminology for what causes - or allows - players to interfere with geometry in old games. Famously, ID's Quake3 gave birth to a whole community of people breaking the physics by jumping, sliding, getting stuck and launching themselves off points in geometry. Some months ago (though I'd be darned if I can find it again!) I saw a conference held by Bungie's Vic DeLeon and a colleague in which Vic briefly discussed the issues he ran into while attempting to wrap 'collision' objects (please correct my terminology) around environment objects so that players could appear as though they were walking on organic surfaces, while not clipping through them or appear to be walking on air at certain points, due to complexities in the modeling. My aim is to compose a case study essay for University in which I can tackle this issue in games, drawing on early exploits and how techniques have changed to address such exploits and to aid in the gameplay itself. I have 3 current day example of where exploits still exist, however specifically targeting ID Software clearly shows they've massively improved their techniques between Q3 and Q4. So in summary, with your help please, I'd like to gain a slightly better understanding of this issue as a whole (its terminology mainly) so I can use terms and ask the right questions within the right contexts. In practical application, I know what it is, I know how to do it, but I don't have the benefit of level design knowledge yet and its technical widgety knick-knack terms =) Many thanks in advance AJ

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• XNA Diffuse Shader Issue. Edge lighting problem. Image Attached

  - by adtither

  As you can see in this image the diffuse shading is working correctly in some places but in other places such as the the bottom of the sphere you can see the squares/triangles of the mesh. Any idea what would be causing this? Let me know if you need anymore information related to code. I can upload my normals calculations and shader effect if required. EDIT: Here's a link to the shader I'm using http://pastebin.com/gymVc7CP Link to normals calculations: http://pastebin.com/KnMGdzHP Seems to be an issue with edge lighting. Can't seem to see where I'm going wrong with the normals calculations though.

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• How to implement Fog Of War with an shader?

  - by Cambrano

  Okay, I'm creating a RTS game and want to implement an AgeOfEmpires-like Fog Of War(FOW). That means a tile(or pixel) can be: 0% transparent (unexplored) 50% transparent black (explored but not in viewrange) 100% transparent(explored and in viewrange) RTS means I'll have many explorers (NPCs, buildings, ...). Okay, so I have an 2d array of bytes byte[,] explored. The byte value correlates the transparency. The question is, how do I pass this array to my shader? Well I think it is not possible to pass an entire array. So: what technique shall I use to let my shader know if a pixel/tile is visible or not?

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