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• How can I do fast Triangle/Square vs Triangle collision detection?

  - by Ólafur Waage

  I have a game world where the objects are in a grid based environment with the following restrictions. All of the triangles are 45-90-45 triangles that are unit length. They can only rotate 90°. The squares are of unit length and can not rotate (not that it matters) I have the Square vs Square detection down and it is very very solid and very fast (max vs min on x and y values) Wondering if there are any tricks I can employ since I have these restrictions on the triangles?

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• collision detection in cocos2d.

  - by seenu

  i want to detect collision detection two times in same row. for example:-(see the below image) the ellipse and rectangle or detcted. after that my ellipse will travelling in the straight line path to down and detect the another rectangle. first one is( travelled in trajectory path ) working fine. second one i want to pass in straight line to down for collision detection. how to do this process.

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• SOM for Detection

  - by Tim

  I would like to know how I can use SOM for disease detection. Given a lung cancer dataset, how can SOM be applied for detection, there are certain terminologies like, sensitivity, specificity and accuracy percentages....are there ways to calculate all these with the SOM algorithm? I would appreciate answers from anyone who can shed more light on this

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• The SQL Beat Podcast-Capturing a SQL Rockstar

  - by SQLBeat

    This is the first permissible (waiting for signed disclaimers) episode of the SQL Beat Podcast featuring the gracious and famous Thomas La Rock. We talk about gay marriage, abortion, SQL community and a 9 inch pipe with a hole in it at the tip. No really. If there ever was a gentleman, SQL Rockstar is one and I want to thank him from the bottom of my digital recorder for agreeing to talk to me and my audience. All forty of them will appreciate the candor. Enjoy World. I did. Oh and a special rock start drum intro from me to you. CLICK HERE TO PLAY >>

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• The SQL Beat Podcast–Capturing a SQL Rockstar

  - by SQLBeat

    This is the first permissible (waiting for signed disclaimers) episode of the SQL Beat Podcast featuring the gracious and famous Thomas La Rock. We talk about gay marriage, abortion, SQL community and a 9 inch pipe with a hole in it at the tip. No really. If there ever was a gentleman, SQL Rockstar is one and I want to thank him from the bottom of my digital recorder for agreeing to talk to me and my audience. All forty of them will appreciate the candor. Enjoy World. I did. Oh and a special rock start drum intro from me to you. CLICK BELOW TO LISTEN >>>>>>>>>CLICK HERE TO PLAY >>>>>>>>> CLICK ABOVE TO SPEAR A FISH INSTEAD

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• The SQL Beat Podcast-Capturing a SQL Rockstar

  - by SQLBeat

  This is the first permissible (waiting for signed disclaimers) episode of the SQL Beat Podcast featuring the gracious and famous Thomas La Rock. We talk about gay marriage, abortion, SQL community and generally convivial and ergonomic as will be witnessed by THAT LONG PIPE IN THE CHAIR. If there ever was a gentleman, SQL Rockstar is one and I want to thank him from the bottom of my digital recorder for agreeing to talk to me and my audience. All forty of them will appreciate the candor. Enjoy World. I did. Oh and a special rock start drum intro from me to you. CLICK HERE TO PLAY

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• Ball to Ball Collision - Detection and Handling

  - by Simucal

  With the help of the Stack Overflow community I've written a pretty basic-but fun physics simulator. You click and drag the mouse to launch a ball. It will bounce around and eventually stop on the "floor". My next big feature I want to add in is ball to ball collision. The ball's movement is broken up into a x and y speed vector. I have gravity (small reduction of the y vector each step), I have friction (small reduction of both vectors each collision with a wall). The balls honestly move around in a surprisingly realistic way. I guess my question has two parts: What is the best method to detect ball to ball collision? Do I just have an O(n^2) loop that iterates over each ball and checks every other ball to see if it's radius overlaps? What equations do I use to handle the ball to ball collisions? Physics 101 How does it effect the two balls speed x/y vectors? What is the resulting direction the two balls head off in? How do I apply this to each ball? Handling the collision detection of the "walls" and the resulting vector changes were easy but I see more complications with ball-ball collisions. With walls I simply had to take the negative of the appropriate x or y vector and off it would go in the correct direction. With balls I don't think it is that way. Some quick clarifications: for simplicity I'm ok with a perfectly elastic collision for now, also all my balls have the same mass right now, but I might change that in the future. In case anyone is interested in playing with the simulator I have made so far, I've uploaded the source here (EDIT: Check the updated source below). Edit: Resources I have found useful 2d Ball physics with vectors: 2-Dimensional Collisions Without Trigonometry.pdf 2d Ball collision detection example: Adding Collision Detection Success! I have the ball collision detection and response working great! Relevant code: Collision Detection: for (int i = 0; i < ballCount; i++) { for (int j = i + 1; j < ballCount; j++) { if (balls[i].colliding(balls[j])) { balls[i].resolveCollision(balls[j]); } } } This will check for collisions between every ball but skip redundant checks (if you have to check if ball 1 collides with ball 2 then you don't need to check if ball 2 collides with ball 1. Also, it skips checking for collisions with itself). Then, in my ball class I have my colliding() and resolveCollision() methods: public boolean colliding(Ball ball) { float xd = position.getX() - ball.position.getX(); float yd = position.getY() - ball.position.getY(); float sumRadius = getRadius() + ball.getRadius(); float sqrRadius = sumRadius * sumRadius; float distSqr = (xd * xd) + (yd * yd); if (distSqr <= sqrRadius) { return true; } return false; } public void resolveCollision(Ball ball) { // get the mtd Vector2d delta = (position.subtract(ball.position)); float d = delta.getLength(); // minimum translation distance to push balls apart after intersecting Vector2d mtd = delta.multiply(((getRadius() + ball.getRadius())-d)/d); // resolve intersection -- // inverse mass quantities float im1 = 1 / getMass(); float im2 = 1 / ball.getMass(); // push-pull them apart based off their mass position = position.add(mtd.multiply(im1 / (im1 + im2))); ball.position = ball.position.subtract(mtd.multiply(im2 / (im1 + im2))); // impact speed Vector2d v = (this.velocity.subtract(ball.velocity)); float vn = v.dot(mtd.normalize()); // sphere intersecting but moving away from each other already if (vn > 0.0f) return; // collision impulse float i = (-(1.0f + Constants.restitution) * vn) / (im1 + im2); Vector2d impulse = mtd.multiply(i); // change in momentum this.velocity = this.velocity.add(impulse.multiply(im1)); ball.velocity = ball.velocity.subtract(impulse.multiply(im2)); } Source Code: Complete source for ball to ball collider. Binary: Compiled binary in case you just want to try bouncing some balls around. If anyone has some suggestions for how to improve this basic physics simulator let me know! One thing I have yet to add is angular momentum so the balls will roll more realistically. Any other suggestions? Leave a comment!

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• Detection of battery status totally messed up

  - by Faabiioo

  I already posted this question in the Ubuntu forum and stackOverflow. I forward it here with the hope to find some different opinions about the problem. I have an Acer TravelMate 5730, which is 3 y.o., running Ubuntu 10.04 LTS. One year ago I changed the battery because the old one died. Since then, everything worked like a charm. A week ago I was using my laptop running on battery; it was charged up to 60%. Suddenly it shut down and for about 24h it was like the battery was totally broken: it didn't charge anymore and the 'upower --dump' said state: critical. I was kind of resigned to buy a new battery, when suddenly the orange light became green: battery was charged and actually working; strangely the battery indicator was stuck to 100%, even after 2 hours running. I tried again with 'upower --dump' or 'acpi -b' commands and it kept saying battery is discharging, though maintaining the percentage to 100%. Thus, battery working fine up to 3 hours, without any warning when it was almost empty, likely to result in a brute shut down. Today something different. the 'upower --dump' command says: ... present: yes rechargeable: yes state: fully-charged energy: 0 Wh energy-empty: 0 Wh energy-full: 65.12 Wh energy-full-design: 65.12 Wh energy-rate: 0 W voltage: 14.481 V percentage: 0% capacity: 100% technology: lithium-ion I tried to boot WinXP and the problem is pretty much the same, with the battery fully-charged, percentage equal to 0% and no way to fix it. While writing, the situation has changed again: present: yes rechargeable: yes state: charging energy: 0 Wh energy-empty: 0 Wh energy-full: 65.12 Wh energy-full-design: 65.12 Wh energy-rate: 0 W voltage: 14.474 V percentage: 0% capacity: 100% technology: lithium-ion ...charging, but it does not charge up. (Recall, the battery lasted 3 hours until yesterday!). So, the big question is: is it an hardware issue, like a dedicated internal circuit is broken? or maybe it is just the battery that must be changed. Or, rather, some BIOS problem that could be fixed in some way. I'd appreciate every help that can shed some light on this annoying problem thanks

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• Rails Browser Detection Methods

  - by alvincrespo

  Hey Everyone, I was wondering what methods are standard within the industry to do browser detection in Rails? Is there a gem, library or sample code somewhere that can help determine the browser and apply a class or id to the body element of the (X)HTML? Thanks, I'm just wondering what everyone uses and whether there is accepted method of doing this? I know that we can get the user.agent and parse that string, but I'm not sure if that is that is an acceptable way to do browser detection. Also, I'm not trying to debate feature detection here, I've read multiple answers for that on StackOverflow, all I'm asking for is what you guys have done. [UPDATE] So thanks to faunzy on GitHub, I've sort of understand a bit about checking the user agent in Rails, but still not sure if this is the best way to go about it in Rails 3. But here is what I've gotten so far: def users_browser user_agent = request.env['HTTP_USER_AGENT'].downcase @users_browser ||= begin if user_agent.index('msie') && !user_agent.index('opera') && !user_agent.index('webtv') 'ie'+user_agent[user_agent.index('msie')+5].chr elsif user_agent.index('gecko/') 'gecko' elsif user_agent.index('opera') 'opera' elsif user_agent.index('konqueror') 'konqueror' elsif user_agent.index('ipod') 'ipod' elsif user_agent.index('ipad') 'ipad' elsif user_agent.index('iphone') 'iphone' elsif user_agent.index('chrome/') 'chrome' elsif user_agent.index('applewebkit/') 'safari' elsif user_agent.index('googlebot/') 'googlebot' elsif user_agent.index('msnbot') 'msnbot' elsif user_agent.index('yahoo! slurp') 'yahoobot' #Everything thinks it's mozilla, so this goes last elsif user_agent.index('mozilla/') 'gecko' else 'unknown' end end return @users_browser end

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• What datastructure would you use for a collision-detection in a tilemap?

  - by Solom

  Currently I save those blocks in my map that could be colliding with the player in a HashMap (Vector2, Block). So the Vector2 represents the coordinates of the blog. Whenever the player moves I then iterate over all these Blocks (that are in a specific range around the player) and check if a collision happened. This was my first rough idea on how to implement the collision-detection. Currently if the player moves I put more and more blocks in the HashMap until a specific "upper bound", then I clear it and start over. I was fully aware that it was not the brightest solution for the problem, but as said, it was a rough first implementation (I'm still learning a lot about game-design and the data-structure). What data-structure would you use to save the Blocks? I thought about a Queue or even a Stack, but I'm not sure, hence I ask.

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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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• What collision detection approach for top down car game?

  - by nathan

  I have a quite advanced top down car game and i use masks to detect collisions. I have the actual designed track (what the player see) with fancy graphics etc. and two other pictures i use as mask for my detection collisions. Each mask has only two colors, white and black and i check each frame if a pixel of the car collide with a black pixel of the masks. This approach works of course but it's not really flexible. Whenever i want to change the look of a track, i have to redraw the mask and it's a real pain. What is the general approach for this kind of game? How can i improve the flexibility of such a mask based approach?

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• Is there a good way to get pixel-perfect collision detection in XNA?

  - by ashes999

  Is there a well-known way (or perhaps reusable bit of code) for pixel-perfect collision detection in XNA? I assume this would also use polygons (boxes/triangles/circles) for a first-pass, quick-test for collisions, and if that test indicated a collision, it would then search for a per-pixel collision. This can be complicated, because we have to account for scale, rotation, and transparency. WARNING: If you're using the sample code from the link from the answer below, be aware that the scaling of the matrix is commented out for good reason. You don't need to uncomment it out to get scaling to work.

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• How can i get almost pixel perfect collision detection in a multiplayer game?

  - by Freddy

  I'm currently working on a multiplayer game for iPhone. The problem i have, as with all multiplayer games, is that the other user will always see everything at a non-constant delay. The game I'm making need to have a almost pixel perfect collision detection, but 1 or 2 pixels off is not that big of a deal. How can I possibly get this working? I guess I could just set local player to also be at X ms delay. However this will probably just be worse and feel sloppy when the user input. I know this problem is probably something network programmers deal with everyday and I would be glad if someone could give me a possible solution for this.

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• Would it be more efficient to handle 2D collision detection with polygons, rather than both squares/polygons?

  - by KleptoKat

  I'm working on a 2D game engine and I'm trying to get collision detection as efficient as possible. One thing I've noted is that I have a Rectangle Collision collider, a Shape (polygon) collider and a circle collider. Would it be more efficient (either dev-time wise or runtime wise) to have just one shape collider, rather than have that and everything else? I feel it would optimize my code in the back end, but how much would it affect my game at runtime? Should I be concerned with this at all, as 3D games generally have tens of thousands of polygons?

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• Welcome to the Java Training Beat!

  - by tmcginn

  We are a group of dedicated training developers for Java, located in the US, India, and now Mexico. In this blog we will announce new training content and events that might be of interest to our readers. In this first installment of the Java Training Beat, I would like to introduce three new Oracle By Example (OBE) modules I recently released and posted to the Oracle Online Learning Library. Creating a Simple Java Message Service (JMS) Producer with NetBeans and GlassFish - covers how to create a simple text message producer with NetBeans 7 and GlassFish. Creating Java Message Service (JMS) Resources in WebLogic Server 12c - covers how to create JMS resources using the console and WebLogic Server 12c. With this tutorial, you can replicate the results of the first tutorial in WebLogic. Creating a Publish/Subscribe Model with Message-Driven Beans and GlassFish Server - covers how to create a publish/subscribe application using JMS. This tutorial includes a short case study that includes a JSF front-end application that sends a hotel reservation request object to the server as a MapMessage. Hope you find these useful!  And do check out the Online Learning Library - we have a wide range of additional content posted and more being added every month!

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• Sub Rectangle or ROI problem in opencv

  - by iva123

  Hi, I'm trying to convert this c code(http://nashruddin.com/OpenCV_Eye_Detection) to the python code, but in c style, he used cvROI thing, since ROI functions are not supported by python-opencv, I tried cvGetSubRect so Here is the eye detection part of the code : eye_region = cvGetSubRect(image,cvRect(face.x,int(face.y + (face.height/4)),face.width,int(face.height/2))) eyes = cvHaarDetectObjects(eye_region,eyeCascade,memo,1.15,3,0,cvSize(25,15)) for e in eyes: cvRectangle(image, cvPoint( int(e.x), int(e.y)), cvPoint(int(e.x + e.width), int(e.y + e.height)), CV_RGB(0, 255, 0), 1, 8, 0) return image; When I run this code, It draws rectangles irrelevant places. I thought, eye_region coordinates are wrong, and tried some coordinates, but it didn't work. Any idea ? Note :Face detection method works very well, and it's code is same with the eye detection method.

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• Collision Detection - Java - Rectangle

  - by Trizicus

  I would like to know if this is a good idea that conforms to best practices that does not lead to obscenely confusing code or major performance hit(s): Make my own Collision detection class that extends Rectangle class. Then when instantiating that object doing something such as Collision col = new Rectangle(); <- Should I do that or is that something that should be avoided? I am aware that I 'can' but should I? I want to extend Rectangle class because of the contains() and intersects() methods; should I be doing that or should I be doing something else for 2D collision detection in Java?

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• Adaboost algorithm and its usage in face detection

  - by Hani

  I am trying to understand Adaboost algorithm but i have some troubles. After reading about Adaboost i realized that it is a classification algorithm(somehow like neural network). But i could not know how the weak classifiers are chosen (i think they are haar-like features for face detection) and how finally the H result which is the final strong classifier can be used. I mean if i found the alpha values and compute the H ,how am i going to benefit from it as a value (one or zero) for new images. Please is there an example describes it in a perfect way? i found the plus and minus example that is found in most adaboost tutorials but i did not know how exactly hi is chosen and how to adopt the same concept on face detection. I read many papers and i had many ideas but until now my ideas are not well arranged. Thanks....

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• What is better: CSS hacks or browser detection?

  - by Darryl Hein

  Commonly when I look around the Internet, I find that people are generally using CSS hacks to make their website look the same in all browsers. Personally, I have found this to be quite time consuming to find all of these hacks and test them; each change you make you have to test in 4+ browsers to make sure it didn't break anything else. About a year ago, I looked around the Internet for what other major sites are using (Yahoo, Google, BBC, etc) and found that most of them are doing some form of browser detection (JS, HTML if statements, server based). I have started doing this as well. On almost all of the sites I have worked on recently, I use jQuery, so I use the built in browser detection. Is there a reason you use or don't use either of these?

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• Where should I place my reaction code in Per-Pixel Collision Detection?

  - by CJ Cohorst

  I have this collision detection code: public bool PerPixelCollision(Player player, Game1 dog) { Matrix atob = player.Transform * Matrix.Invert(dog.Transform); Vector2 stepX = Vector2.TransformNormal(Vector2.UnitX, atob); Vector2 stepY = Vector2.TransformNormal(Vector2.UnitY, atob); Vector2 iBPos = Vector2.Transform(Vector2.Zero, atob); for(int deltax = 0; deltax < player.playerTexture.Width; deltax++) { Vector2 bpos = iBPos; for (int deltay = 0; deltay < player.playerTexture.Height; deltay++) { int bx = (int)bpos.X; int by = (int)bpos.Y; if (bx >= 0 && bx < dog.dogTexture.Width && by >= 0 && by < dog.dogTexture.Height) { if (player.TextureData[deltax + deltay * player.playerTexture.Width].A > 150 && dog.TextureData[bx + by * dog.Texture.Width].A > 150) { return true; } } bpos += stepY; } iBPos += stepX; } return false; } What I want to know is where to put in the code where something happens. For example, I want to put in player.playerPosition.X -= 200 just as a test, but I don't know where to put it. I tried putting it under the return true and above it, but under it, it said unreachable code, and above it nothing happened. I also tried putting it by bpos += stepY; but that didn't work either. Where do I put the code?

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• Huge dataset point in polygon in .net (collision detection)

  - by Rickard Liljeberg

  I have a pretty big mesh with polygons, usually triangles but sometimes rectangles. Each point in my mesh has a value (value has nothing to do with coordinates). Now I am creating a second mesh in the same coordinate-space as the old mesh. I now want to interpolate out values for all points (vertices) in the new mesh using the values from the old mesh. Now I could loop each polygon in the new mesh and detect which old vertices are in each polygon by making 2d collision detection (altho even this I don't get to function properly so if anyone has simple and fast code for 2d collision detection (triangle is enough) I would gladly see it). However to my main point again. looping each old vertice for each new polygon seems less than efficient. is there a better way?

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• How to choose cell to put entity in in an uniform grid used for broad phase collision detection?

  - by nathan

  I'm trying to implement the broad phase of my collision detection algorithm. My game is an arcade game with lot of moving entities in an open space with relatively equivalent sizes. Regarding the above specifications, i decided to use an uniform grid for space partitioning. The problem i have right know is how to efficiently choose in which cells an entity should be added. ATM i'm doing something like this: for (int x = 0; x < gridSize; x++) { for (int y = 0; y < gridSize; y++) { GridCell cell = grid[x][y]; cell.clear(); //remove the previously added entities for (int i = 0; i < entities.size(); i++) { Entity e = entities.get(i); if (cell.isEntityOverlap(e)) { cell.add(e); } } } } The isEntityOverlap is a simple method i added my GridCell class. public boolean isEntityOverlap(Shape s) { return cellArea.intersects(s); } Where cellArea is a Rectangle. cellArea = new Rectangle(x, y, CollisionGrid.CELL_SIZE, CollisionGrid.CELL_SIZE); It works but it's damn slow. What would be a fast way to know all the cells an entity overlaps? Note: by "it works" i mean, the entities are contained in the good cells over the time after movements etc.

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• Using CGRectIntersectsRect for collision detection

  - by user309030

  Hi guys, I've got a long rectangular image which is rotated at different kind of angles. However the frame of the rectangular image does not rotate along with the image and instead, the rotation causes the frame to to become larger to fit the rotated image. So when I used CGRectIntersectsRect, the collision detection is totally off because the other image colliding with the rectangular image will collide before it even reaches the visible area of the rect image. In case you don't really know what I'm talking about, have a look at the ascii drawing: normal rectangular image frame, O - pixels, |, – - frame |----------| |OOOOOOOOOO| |----------| after rotation |----------| |O | | O | | O | | O | | O | | O | | O | | O | | O | |----------| I've read through some of the collision articles but all of them are talking about collision with a normal straight rectangle and what I really want is collision with a slanted image, preferably pixel collision detection. TIA for any suggestions made.

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• Opinions on collision detection objects with a moving scene

  - by Evan Teran

  So my question is simple, and I guess it boils down to how anal you want to be about collision detection. To keep things simple, lets assume we're talking about 2D sprites defined by a bounding box. In addition, let's assume that my sprite object has a function to detect collisions like this: S.collidesWith(other); Finally the scene is moving and "walls" in the scene can move, an object may not touch a wall. So a simple implementation might look like this (psuedo code): moveWalls(); moveSprite(); foreach(wall as w) { if(s.collidesWith(w)) { gameover(); } } The problem with this is that if the sprite and wall move towards each other, depending on the circumstances (such as diagonal moment). They may pass though each other (unlikely but could happen). So I may do this instead. moveWalls(); foreach(wall as w) { if(s.collidesWith(w)) { gameover(); } } moveSprite(); foreach(wall as w) { if(s.collidesWith(w)) { gameover(); } } This takes care of the passing through each other issue, but another rare issue comes up. If they are adjacent to each other (literally the next pixel) and both the wall and the sprite are moving left, then I will get an invalid collision since the wall moves, checks for collision (hit) then the sprite is moved. Which seems unfair. In addition, to that, the redundant collision detection feels very inefficient. I could give the player movement priority alleviating the first issue but it is still checking twice. moveSprite(); foreach(wall as w) { if(s.collidesWith(w)) { gameover(); } } moveWalls(); foreach(wall as w) { if(s.collidesWith(w)) { gameover(); } } Am I simply over thinking this issue, should this just be chalked up to "it'll happen rare enough that no one will care"? Certainly looking at old sprite based games, I often find situations where the collision detection has subtle flaws, but I figure by now we can do better :-P. What are people's thoughts?

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