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• Orthographic unit translation mismatch on grid (e.g. 64 pixels translates incorrectly)

  - by Justin Van Horne

  I am looking for some insight into a small problem with unit translations on a grid. Setup 512x448 window 64x64 grid gl_Position = projection * world * position; projection is defined by ortho(-w/2.0f, w/2.0f, -h/2.0f, h/2.0f); This is a textbook orthogonal projection function. world is defined by a fixed camera position at (0, 0) position is defined by the sprite's position. Problem In the screenshot below (1:1 scaling) the grid spacing is 64x64 and I am drawing the unit at (64, 64), however the unit draws roughly ~10px in the wrong position. I've tried uniform window dimensions to prevent any distortion on the pixel size, but now I am a bit lost in the proper way in providing a 1:1 pixel-to-world-unit projection. Anyhow, here are some quick images to aide in the problem. I decided to super-impose a bunch of the sprites at what the engine believes is 64x offsets. When this seemed off place, I went about and did the base case of 1 unit. Which seemed to line up as expected. The yellow shows a 1px difference in the movement. Vertices It would appear that the vertices going into the vertex shader are correct. For example, in reference to the first image the data looks like this in the VBO: x y x y ---------------------------- tl | 0.0 24.0 64.0 24.0 bl | 0.0 0.0 -> 64.0 0.0 tr | 16.0 0.0 80.0 0.0 br | 16.0 24.0 80.0 24.0 With that said, all I am left to believe is that I am munging up my actual projection. So, I am looking for any insight into maintaining the 1:1 pixel-to-world-unit projection.

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• Transforming a primitive tetrahedron into a primitive icosahedron?

  - by Djentleman

  I've created a tetrahedron by creating a BoundingBox and building the faces of the tetrahedron within the bounding box as follows (see image as well): VertexPositionNormalTexture[] vertices = new VertexPositionNormalTexture[12]; BoundingBox box = new BoundingBox(new Vector3(-1f, 1f, 1f), new Vector3(1f, -1f, -1f)); vertices[0].Position = box.GetCorners()[0]; vertices[1].Position = box.GetCorners()[2]; vertices[2].Position = box.GetCorners()[7]; vertices[3].Position = box.GetCorners()[0]; vertices[4].Position = box.GetCorners()[5]; vertices[5].Position = box.GetCorners()[2]; vertices[6].Position = box.GetCorners()[5]; vertices[7].Position = box.GetCorners()[7]; vertices[8].Position = box.GetCorners()[2]; vertices[9].Position = box.GetCorners()[5]; vertices[10].Position = box.GetCorners()[0]; vertices[11].Position = box.GetCorners()[7]; What would I then have to do to transform this tetrahedron into an icosahedron? Similar to this image: I understand the concept but applying it is another thing entirely for me.

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• Rotate an image in a scaled context

  - by nathan

  Here is my working piece of code to rotate an image toward a point (in my case, the mouse cursor). float dx = newx - ploc.x; float dy = newy - ploc.y; float angle = (float) Math.toDegrees(Math.atan2(dy, dx)); Where ploc is the location of the image i'm rotating. And here is the rendering code: g.rotate(loc.x + width / 2, loc.y + height / 2, angle); g.drawImage(frame, loc.x, loc.y); Where loc is the location of the image and "width" and "height" are respectively the width and height of the image. What changes are needed to make it works on a scaled context? e.g make it works with something like g.scale(sx, sy).

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• Where can I find free or buy "next-gen" 3D Assets?

  - by Valmond

  Usually I buy 3D Assets from sites like turbosquid.com or similar. My problem is that I have lately implemented glow, normal maps, specular (and specular power) maps and reflection maps and I can't find any models that use those techniques. So where can I find / buy "next gen" assets (at least models/items with a normal map)? I have checked for similar posts but those I found are about either free only or 2D or 'ordinary' 3D so I hope this is not a duplicate.

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• Breakout clone, how to handle/design for collision detection/physics between objects?

  - by Zolomon

  I'm working on a breakout clone, and I wish to create some realistic physics effects for collision - angles on the paddle should allow the ball to bounce, as well as doing curve balls etc. I could use per-pixel based collision detection, but then I thought it might be easier with line/circle intersection testing. So, then I naturally consider making a polygon class for the line-based objects and use the built-in circle class for the circular objects. That sounds like an OK approach, right? And then just check for collision using the specified algorithm based on the objects that might be within each other's range?

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• Component-based design: handling objects interaction

  - by Milo

  I'm not sure how exactly objects do things to other objects in a component based design. Say I have an Obj class. I do: Obj obj; obj.add(new Position()); obj.add(new Physics()); How could I then have another object not only move the ball but have those physics applied. I'm not looking for implementation details but rather abstractly how objects communicate. In an entity based design, you might just have: obj1.emitForceOn(obj2,5.0,0.0,0.0); Any article or explanation to get a better grasp on a component driven design and how to do basic things would be really helpful.

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• Translating an Object to a certain Vector 3 in OpenGL and Java LWJGL

  - by aliasmk

  So after almost two hours, I got the hang of using glTranslated() (with Java and LWJGL). If I am correct, applying glTranslated on an object moves that object with the x,y,z relative to the previously moved object. I believe the correct term for this is local vs global, global being the one I want. I was wondering if there was a way to translate an object to a specific XYZ position, or relative to the origin. Thanks! (Code or other details can be supplied if it helps, just let me know. Also sorry if this is a noob comment, Im very new to OpenGL.)

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• Cocos2d copied actions not responding?

  - by Stephen

  I am running an animation on 2 sprites like so: -(void) startFootballAnimation { CCAnimation* footballAnim = [CCAnimation animationWithFrame:@"Football" frameCount:60 delay:0.005f]; spiral = [CCAnimate actionWithAnimation:footballAnim]; CCRepeatForever* repeat = [CCRepeatForever actionWithAction:spiral]; [self runAction:repeat]; [secondFootball runAction:[[repeat copy] autorelease]]; } The problem I am having is I call this method: - (void) slowAnimation { [spiral setDuration:[spiral duration] + 0.01]; } and it only slows down the first sprites animation and not the second one. Do I need to do something different with copied actions to get them to react to the slowing of the animation?

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• Robust line of sight test on the inside of a polygon with tolerance

  - by David Gouveia

  Foreword This is a followup to this question and the main problem I'm trying to solve. My current solution is an hack which involves inflating the polygon, and doing most calculations on the inflated polygon instead. My goal is to remove this step completely, and correctly solve the problem with calculations only. Problem Given a concave polygon and treating all of its edges as if they were walls in a level, determine whether two points A and B are in line of sight of each other, while accounting for some degree of floating point errors. I'm currently basing my solution on a series of line-segment interection tests. In other words: If any of the end points are outside the polygon, they are not in line of sight. If both end points are inside the polygon, and the line segment from A to B crosses any of the edges from the polygon, then they are not in line of sight. If both end points are inside the polygon, and the line segment from A to B does not cross any of the edges from the polygon, then they are in line of sight. But the problem is dealing correctly with all the edge cases. In particular, it must be able to deal with all the situations depicted below, where red lines are examples that should be rejected, and green lines are examples that should be accepted. I probably missed a few other situations, such as when the line segment from A to B is colinear with an edge, but one of the end points is outside the polygon. One point of particular interest is the difference between 1 and 9. In both cases, both end points are vertices of the polygon, and there are no edges being intersected, but 1 should be rejected while 9 should be accepted. How to distinguish these two? I could check some middle point within the segment to see if it falls inside or not, but it's easy to come up with situations in which it would fail. Point 7 was also pretty tricky and I had to to treat it as a special case, which checks if two points are adjacent vertices of the polygon directly. But there are also other chances of line segments being col linear with the edges of the polygon, and I'm still not entirely sure how I should handle those cases. Is there any well known solution to this problem?

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• Toon/cel shading with variable line width?

  - by Nick Wiggill

  I see a few broad approaches out there to doing cel shading: Duplication & enlargement of model with flipped normals (not an option for me) Sobel filter / fragment shader approaches to edge detection Stencil buffer approaches to edge detection Geometry (or vertex) shader approaches that calculate face and edge normals Am I correct in assuming the geometry-centric approach gives the greatest amount of control over lighting and line thickness, as well eg. for terrain where you might see the silhouette line of a hill merging gradually into a plain? What if I didn't need pixel lighting on my terrain surfaces? (And I probably won't as I plan to use cell-based vertex- or texturemap-based lighting/shadowing.) Would I then be better off sticking with the geometry-type approach, or go for a screen space / fragment approach instead to keep things simpler? If so, how would I get the "inking" of hills within the mesh silhouette, rather than only the outline of the entire mesh (with no "ink" details inside that outline? Lastly, is it possible to cheaply emulate the flipped-normals approach, using a geometry shader? Is that exactly what the GS approaches do? What I want - varying line thickness with intrusive lines inside the silhouette... What I don't want...

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• Colorize with a given color a texture

  - by Pacha

  I have a texture and I want to "colorize" it with a given color, lets say cyan (#00ffff) or purple (#800080). What I want to do, is get all the pixel values from the texture, and remove the color and keep the "brightness" and "saturation" and apply to the desired color. There is a tool in GIMP to do this called Colorize (Colors -> Colorize.. while editing), I made an example below. This is will all be done in a shader (GLSL), although this is probably a general algorithm.

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• Marketing: Angry Birds - How it's done

  - by John

  Why do some apps, like Angry Birds, dominate the market while other cool/fun/addicting apps are never heard of? I'm trying to figure out the best marketing strategy, or best way to sell an app to mass market. Does anybody have any ideas or things they noticed about the marketing of major blockbuster apps, like Angry Birds, why they get so popular and stay at the top of charts. Thanks for any ideas, comments ...

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• Animate from end frame of one animation to end frame of another Unity3d/C#

  - by Timothy Williams

  So I have two legacy FBX animations; Animation A and Animation B. What I'm looking to do is to be able to fade from A to B regardless of the current frame A is on. Using animation.CrossFade() will play A in reverse until it reaches frame 0, then play B forward. What I'm looking to do is blend from the current frame of A to the end frame of B. Probably via some sort of lerp between the facial position in A and the facial position in the last frame of B. Does anyone know how I might be able to accomplish this? Either via a built in function or potentially lerping of some sort?

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• How is this lighting effect done?

  - by Mike

  This is the most beautiful 2d lighting I have ever seen. Does anyone know how he went about doing it? http://www.youtube.com/watch?v=BIQRhOFkvQY http://www.youtube.com/watch?v=tnTYXPuecMs http://www.youtube.com/watch?v=rhC_jVM8IYU http://www.youtube.com/watch?v=_Aw5BdjWqqU Or download it here: http://grantkot.com/PollutedPlanet/publish.htm edit: I am not asking how the particles are simulated; I don't care about the physics.

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• D3D11 how to simulate multiple depth channels

  - by Nock

  Here's what I'd like to achieve: Rendering a first pass of objects in my scene, using standard depth comparison Rendering another pass of objects in the same scene, but with the following rules: A Pixel of the 2nd pass always override the first pass (no depth compare between them) Use Depth comparison between pixels written from the second pass. In English I want depth comparison made inside each pass but I always want the second pass pixels to override the first pass ones. Some things I've thought: I tried to think about using stencil to solve this, but I couldn't find a way. I know I could render into a separate target the second pass then composite the result into the first, but I'd like to avoid that. I could use two separate Depth Buffer, one dedicated to each pass. (I never tried, but I figure it's possible to switch the depth buffer in a Render Target "on the fly") Any idea of the best solution? Thanks

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• How can I convert an image from raw data in Android without any munging?

  - by stephelton

  I have raw image data (may be png, jpg, ...) and I want it converted in Android without changing its pixel depth (bpp). In particular, when I load a grayscale (8 bpp) image that I want to use as alpha (glTexImage() with GL_ALPHA), it converts it to 16 bpp (presumably 5_6_5). While I do have a plan b (actually, I'm probably on plan 'e' by now, this is really becoming annoying) I would really like to discover an easy way to do this using what is readily available in the api. So far, I'm using BitmapFactory.decodeByteArray(). While I'm at it. I'm doing this from a native environment via jni (passing the buffer in from C, and a new buffer back to C from Java). Any portable solution in C/C++ would be preferable, but I don't want to introduce anything that might break in future versions of Android, etc.

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• Platform jumping problems with AABB collisions

  - by Vee

  See the diagram first: When my AABB physics engine resolves an intersection, it does so by finding the axis where the penetration is smaller, then "push out" the entity on that axis. Considering the "jumping moving left" example: If velocityX is bigger than velocityY, AABB pushes the entity out on the Y axis, effectively stopping the jump (result: the player stops in mid-air). If velocityX is smaller than velocitY (not shown in diagram), the program works as intended, because AABB pushes the entity out on the X axis. How can I solve this problem? Source code: public void Update() { Position += Velocity; Velocity += World.Gravity; List<SSSPBody> toCheck = World.SpatialHash.GetNearbyItems(this); for (int i = 0; i < toCheck.Count; i++) { SSSPBody body = toCheck[i]; body.Test.Color = Color.White; if (body != this && body.Static) { float left = (body.CornerMin.X - CornerMax.X); float right = (body.CornerMax.X - CornerMin.X); float top = (body.CornerMin.Y - CornerMax.Y); float bottom = (body.CornerMax.Y - CornerMin.Y); if (SSSPUtils.AABBIsOverlapping(this, body)) { body.Test.Color = Color.Yellow; Vector2 overlapVector = SSSPUtils.AABBGetOverlapVector(left, right, top, bottom); Position += overlapVector; } if (SSSPUtils.AABBIsCollidingTop(this, body)) { if ((Position.X >= body.CornerMin.X && Position.X <= body.CornerMax.X) && (Position.Y + Height/2f == body.Position.Y - body.Height/2f)) { body.Test.Color = Color.Red; Velocity = new Vector2(Velocity.X, 0); } } } } } public static bool AABBIsOverlapping(SSSPBody mBody1, SSSPBody mBody2) { if(mBody1.CornerMax.X <= mBody2.CornerMin.X || mBody1.CornerMin.X >= mBody2.CornerMax.X) return false; if (mBody1.CornerMax.Y <= mBody2.CornerMin.Y || mBody1.CornerMin.Y >= mBody2.CornerMax.Y) return false; return true; } public static bool AABBIsColliding(SSSPBody mBody1, SSSPBody mBody2) { if (mBody1.CornerMax.X < mBody2.CornerMin.X || mBody1.CornerMin.X > mBody2.CornerMax.X) return false; if (mBody1.CornerMax.Y < mBody2.CornerMin.Y || mBody1.CornerMin.Y > mBody2.CornerMax.Y) return false; return true; } public static bool AABBIsCollidingTop(SSSPBody mBody1, SSSPBody mBody2) { if (mBody1.CornerMax.X < mBody2.CornerMin.X || mBody1.CornerMin.X > mBody2.CornerMax.X) return false; if (mBody1.CornerMax.Y < mBody2.CornerMin.Y || mBody1.CornerMin.Y > mBody2.CornerMax.Y) return false; if(mBody1.CornerMax.Y == mBody2.CornerMin.Y) return true; return false; } public static Vector2 AABBGetOverlapVector(float mLeft, float mRight, float mTop, float mBottom) { Vector2 result = new Vector2(0, 0); if ((mLeft > 0 || mRight < 0) || (mTop > 0 || mBottom < 0)) return result; if (Math.Abs(mLeft) < mRight) result.X = mLeft; else result.X = mRight; if (Math.Abs(mTop) < mBottom) result.Y = mTop; else result.Y = mBottom; if (Math.Abs(result.X) < Math.Abs(result.Y)) result.Y = 0; else result.X = 0; return result; }

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• how to make HLSL effect just for lighning without texture mapping?

  - by naprox

  I'm new to XNA, i created an effect and just want to use lightning but in default effect that XNA create we should do texture mapping or the model appears 'RED', because of this lines of code in the effect file: float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0 { float4 output = float4(1,0,0,1); return output; } and if i want to see my model (appear like when i use basiceffect) must do texture mapping by UV coordinates. but my model does not have UV coordinates assigned or its UV coordinates is not exported. and if i do texture mapping i got error. (i do texture mapping by this line of code in vertexshaderfunction and other necessary codes) output.UV= input.UV i have many of this models and want to work with them.(my models are in .FBX format) when i use Bassiceffect i have no problem and model appears correctly. how can i use "just" lightnings in my custom effects? and don't do texture mapping (because i have no UV coordinates in my models) and my model be look like when i use BasicEffect? if you need my complete code Here it is: http://www.mediafire.com/?4jexhd4ulm2icm2 here is inside of my Model Using BasicEffect http://i.imgur.com/ygP2h.jpg?1 and this is my code for drawing with or without BasicEffect inside of my draw() method: Matrix baseWorld = Matrix.CreateScale(Scale) * Matrix.CreateFromYawPitchRoll(Rotation.Y, Rotation.X, Rotation.Z) * Matrix.CreateTranslation(Position); foreach(ModelMesh mesh in Model.Meshes) { Matrix localWorld = ModelTransforms[mesh.ParentBone.Index] * baseWorld; foreach(ModelMeshPart part in mesh.MeshParts) { Effect effect = part.Effect; if (effect is BasicEffect) { ((BasicEffect)effect).World = localWorld; ((BasicEffect)effect).View = View; ((BasicEffect)effect).Projection = Projection; ((BasicEffect)effect).EnableDefaultLighting(); } else { setEffectParameter(effect, "World", localWorld); setEffectParameter(effect, "View", View); setEffectParameter(effect, "Projection", Projection); setEffectParameter(effect, "CameraPosition", CameraPosition); } } mesh.Draw(); } setEffectParameter is another method that sets effect parameter if i use my custom effect.

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• Tile map collision is not working properly

  - by Sigh-AniDe

  I am having problems setting collision between my sprite and the tiles. I have only done the code for colision for moving upwards but some places on the map it moves up and some places it doesn't. Here is what I have so far: Vector2 position; private static float scalingFactor = 32; static int tileWidth = 32; static int tileHeight = 32; int[ , ] map = { {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, }; // This is in turtle.update if ( keyboardState.IsKeyDown( Keys.Up ) ) { if ( position.Y > screenHeight / 4 ) { //// current position of the turtle on the tiles int mapX = ( int )( position.X / scalingFactor ); int mapY = ( int )( position.Y / scalingFactor ) - 1; if ( isMovable( mapX , mapY , map ) ) { position.Y = position.Y - scalingFactor; } } else { MoveUp(); } } private void MoveUp() { motion.Y = -1; } public bool isMovable( int mapX , int mapY , int[ , ] map ) { if ( mapX < 0 || mapX > 19 || mapY < 0 || mapY > 20 ) { return false; } int tile = map[ mapX , mapY ]; if ( tile == 0 ) { return false; } return true; } protected override void Update( GameTime gameTime ) { turtle.Update( screenHeight , scalingFactor , map ); base.Update( gameTime ); }

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• Jumping with Mecanim synchronization

  - by Abhishek Deb

  I am using Unity3D 4.1 for one of my projects. I have a robot character which is always running. I am using mecanim animation system. What I really want:When I press Space bar, the character should jump up in the air, triggering an animation clip and then by the time it reaches the ground, the animation clip should also end. What actually is happening:When I press Space bar, the character jumps in the air. Animation clip plays as it should, but ends way before it reaches the ground. So, it looks like he is running in the mid air. What have I done: I have this humanoid robot setup with a jump animation bounded with the space bar key. Also, instead of using root motion, I am directly moving the robot from code. //Jumping if(Input.GetKeyDown(KeyCode.Space)){ rigidbody.AddForce(Vector3.up*jumpVelocty); anim.SetBool("Jump",true); } else anim.SetBool("Jump",false); Character's Details: Rigidbody = Mass:30, Freeze rotaion:x,y,z Capsule Collider = Material: metal, center(0,4.5,0), radius:1, height:11 Script = jumpVelocity:20000 Jump Animation Clip: ~ 2 seconds. I am really out of ideas how to synchronize everything. Should I make the character jump in some other way so that it quickly comes down and touches the ground to match the animation clip? If yes, please provide a direction.

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• What features does D3D have that OpenGL does not (and vice versa)?

  - by Tom

  Are there any feature comparisons on Direct3D 11 and the newest OpenGL versions? Well, simply put, Direct3D 11 introduced three main features (taken from Wikipedia): Tesselation Multithreaded rendering Compute shaders Increased texture cache Now I'm wondering, how does the newest versions of OpenGL cope with these features? And since I have this feeling that there are features that Direct3D lacks from OpenGL's side, what are those?

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• How can I make the camera return to the beginning of the terrain when it reaches the end?

  - by wbaccari

  How can I make the camera return to the beginning of the terrain when it reaches the end? I tried using the ICameraSceneNode*-setPosition(). if (camera->getPosition().X>1200.f) camera->setPosition(vector3df(1.f,1550.f,camera->getPosition().Z)); if (camera->getPosition().X<0.f) camera->setPosition(vector3df(1199.f,1550.f,camera->getPosition().Z)); if (camera->getPosition().Z>1200.f) camera->setPosition(vector3df(camera->getPosition().X,1550.f,1.f)); if (camera->getPosition().Z<0.f) camera->setPosition(vector3df(camera->getPosition().X,1550.f,1199.f)); It seems to work fine with a flat terrain (one shade of grey in heightmap) but it starts to produce a strange behavior as soon as i try to add some hills. Edit: The setPosition() call seems to perform a translation of the camera toward the new position, therefore the camera stops at the first obstacle it encounters on its way.

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• effect and model vertex declaration compatibility

  - by Vodácek

  I have normal model drawing code. When I try to draw model without UV coordinates I got this exception: System.InvalidOperationException: The current vertex declaration does not include all the elements required by the current vertex shader. TextureCoordinate0 is missing. at Microsoft.Xna.Framework.Graphics.GraphicsDevice.VerifyCanDraw( Boolean bUserPrimitives, Boolean bIndexedPrimitives) at Microsoft.Xna.Framework.Graphics.GraphicsDevice.DrawIndexedPrimitives( PrimitiveType primitiveType, Int32 baseVertex, Int32 minVertexIndex, Int32 numVertices, Int32 startIndex, Int32 primitiveCount) at Microsoft.Xna.Framework.Graphics.ModelMeshPart.Draw() at Microsoft.Xna.Framework.Graphics.ModelMesh.Draw() ... I know what cause the exception, but is possible to avoid it? Is possible to check model before drawing it with current shader for vertex declaration compatibility?

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• Splitting Graph into distinct polygons in O(E) complexity

  - by Arthur Wulf White

  If you have seen my last question: trapped inside a Graph : Find paths along edges that do not cross any edges How do you split an entire graph into distinct shapes 'trapped' inside the graph(like the ones described in my last question) with good complexity? What I am doing now is iterating over all edges and then starting to traverse while always taking the rightmost turn. This does split the graph into distinct shapes. Then I eliminate all the excess shapes (that are repeats of previous shapes) and return the result. The complexity of this algorithm is O(E^2). I am wondering if I could do it in O(E) by removing edges I already traversed previously. My current implementation of that returns unexpected results.

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• Stencil buffer appears to not be decrementing values correctly

  - by Alex Ames

  I'm attempting to use the stencil buffer as a clipper for my UI system, but I'm having trouble debugging a problem I'm running in to. This is what I'm doing: A widget can pass a rectangle to the the stencil clipper functions, which will increment the stencil buffer values that it covers. Then it will draw its children, which will only get drawn in the stencilled area (so that if they extend outside they'll be clipped). After a widget is done drawing its children, it pops that rectangle from the stack and in the process decrements the values in the stencil buffer that it has previously incremented. The slightly simplified code is below: static void drawStencil(Rect& rect, unsigned int ref) { // Save previous values of the color and depth masks GLboolean colorMask[4]; GLboolean depthMask; glGetBooleanv(GL_COLOR_WRITEMASK, colorMask); glGetBooleanv(GL_DEPTH_WRITEMASK, &depthMask); // Turn off drawing glColorMask(0, 0, 0, 0); glDepthMask(0); // Draw vertices here ... // Turn everything back on glColorMask(colorMask[0], colorMask[1], colorMask[2], colorMask[3]); glDepthMask(depthMask); // Only render pixels in areas where the stencil buffer value == ref glStencilFunc(GL_EQUAL, ref, 0xFF); glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP); } void pushScissor(Rect rect) { // increment things only at the current stencil stack level glStencilFunc(GL_EQUAL, s_scissorStack.size(), 0xFF); glStencilOp(GL_KEEP, GL_INCR, GL_INCR); s_scissorStack.push_back(rect); drawStencil(rect, states, s_ScissorStack.size()); } void popScissor() { // undo what was done in the previous push, // decrement things only at the current stencil stack level glStencilFunc(GL_EQUAL, s_scissorStack.size(), 0xFF); glStencilOp(GL_KEEP, GL_DECR, GL_DECR); Rect rect = s_scissorStack.back(); s_scissorStack.pop_back(); drawStencil(rect, states, s_scissorStack.size()); } And this is how it's being used by the Widgets if (m_clip) pushScissor(m_rect); drawInternal(target, states); for (auto child : m_children) target.draw(*child, states); if (m_clip) popScissor(); This is the result of the above code: There are two things on the screen, a giant test button, and a window with some buttons and text areas on it. The text area scroll box is set to clip its children (so that the text doesn't extend outside the scroll box). The button is drawn after the window and should be on top of it completely. However, for some reason the text area is appearing on top of the button. The only reason I can think of that this would happen is if the stencil values were not getting decremented in the pop, and when it comes time to render the button, since those pixels don't have the right stencil value it doesn't draw over. But I can't figure out whats wrong with my code that would cause that to happen.

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