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Stretching a square image onto a rhombus?
Dec 3, 2011 at 10:40pm
Hi,
First off, I'm a noob (sorry). I tried searching the web for a way to do this but haven't had any luck.
What I want to do is take a square image, say 50x50 pixels, and somehow stretch it onto a rhombus with sides of length 50 pixels, so that it's basically like looking at the 2d image from an angle. Also the angle of viewing needs to be variable.
I was thinking that I could write an algorithm for this, where the color of each pixel is the average of the pixels that it would be overlapping if the image were turned at that angle and didn't lose it's original pixellation. However I don't know how well this would work, and it seems like it would be a complicated algorithm to write.
Is there some function out there that's already been written that can do this? Also is it practical to hope that it will run fast enough to draw, say, one hundred rotating images at 60fps? Because if this isn't practical then it won't be worth the trouble anyway.
Thanks in advance,
-Levi
First off, I'm a noob (sorry). I tried searching the web for a way to do this but haven't had any luck.
What I want to do is take a square image, say 50x50 pixels, and somehow stretch it onto a rhombus with sides of length 50 pixels, so that it's basically like looking at the 2d image from an angle. Also the angle of viewing needs to be variable.
I was thinking that I could write an algorithm for this, where the color of each pixel is the average of the pixels that it would be overlapping if the image were turned at that angle and didn't lose it's original pixellation. However I don't know how well this would work, and it seems like it would be a complicated algorithm to write.
Is there some function out there that's already been written that can do this? Also is it practical to hope that it will run fast enough to draw, say, one hundred rotating images at 60fps? Because if this isn't practical then it won't be worth the trouble anyway.
Thanks in advance,
-Levi
Dec 4, 2011 at 12:27am
Wait. Do you want to shear (I'm guessing this is what you meant, since you can't stretch a rectangle into a rhombus), or rotate?
Either way, both can be accomplished using linear transformations, but how you approach it depends on what you're using for graphical output (OpenGL, SDL, images, etc.).
Either way, both can be accomplished using linear transformations, but how you approach it depends on what you're using for graphical output (OpenGL, SDL, images, etc.).
Dec 4, 2011 at 12:34am
No I mean distort the image so that it fits onto a rhombus. In GML there is a system of functions for doing this, but I don't know what it's C++ counterpart is.
More specifically, the top left corner of your image will be in the top left corner of the rhombus, the top right corner of the image will be in the top right of the rhombus, etc., and all the pixels in between are blended so that you can still recognize the image (at least if your rhombus is somewhat close to being a square).
More specifically, the top left corner of your image will be in the top left corner of the rhombus, the top right corner of the image will be in the top right of the rhombus, etc., and all the pixels in between are blended so that you can still recognize the image (at least if your rhombus is somewhat close to being a square).
Last edited on Dec 4, 2011 at 12:36am
Dec 4, 2011 at 12:40am
Sorry, I'm not following. Mainly, I don't understand how what you said is different from a rotation. Can you post a link to the documentation of the functions you're talking about?
Dec 4, 2011 at 12:48am
Well it would be like rotating a 2d (xy plane) image on the z axis orthogonally, if that's what you mean.
Here's the documentation on the functions:
http://gamemaker.info/en/manual/405_06_advanced
Look for the primitive and texture-related functions.
Here's the documentation on the functions:
http://gamemaker.info/en/manual/405_06_advanced
Look for the primitive and texture-related functions.
Dec 4, 2011 at 12:59am
draw_primitive_begin_texture() and draw_vertex_texture(), right? And this is what you want to do:
http://imageshack.us/photo/my-images/4/rotation.png/
Right?
http://imageshack.us/photo/my-images/4/rotation.png/
Right?
Dec 4, 2011 at 1:44am
No I mean from this
http://images.google.com/imgres?q=square&hl=en&safe=off&gbv=2&biw=1366&bih=667&tbm=isch&tbnid=ScFzYm3MSzcdWM:&imgrefurl=http://fixbyproximity.com/2011/07/2d-game-dev-2d-graphic-basics/%3Fprint%3D1&docid=OHI6Cigow5foxM&imgurl=http://fixbyproximity.com/wp-content/uploads/2011/07/square.png&w=500&h=500&ei=etDaTv3iDKKYiQKAzdWIDQ&zoom=1&iact=rc&dur=819&sig=114820397596981472587&page=1&tbnh=138&tbnw=184&start=0&ndsp=21&ved=1t:429,r:2,s:0&tx=59&ty=73
to this
http://images.google.com/imgres?q=rhombus&start=56&num=10&hl=en&safe=off&gbv=2&biw=1366&bih=667&tbm=isch&tbnid=IXv_701d24BJSM:&imgrefurl=http://www.fastgeometry.com/Encyclopedia/Polygons.htm&docid=kVsOTgeinbYEAM&imgurl=http://www.fastgeometry.com/images/rhombus.gif&w=155&h=195&ei=MdDaTv3FB8PXiQLv4PiICg&zoom=1&iact=hc&vpx=721&vpy=392&dur=3152&hovh=156&hovw=124&tx=90&ty=92&sig=114820397596981472587&sqi=2&page=4&tbnh=139&tbnw=111&ndsp=21&ved=1t:429,r:10,s:56
But yes, those are the functions I was referring to. They allow you to take a triangular portion of a picture and stretch it into any other shaped triangle, and by splitting your picture into two triangles you can make a square into a rhombus.
http://images.google.com/imgres?q=square&hl=en&safe=off&gbv=2&biw=1366&bih=667&tbm=isch&tbnid=ScFzYm3MSzcdWM:&imgrefurl=http://fixbyproximity.com/2011/07/2d-game-dev-2d-graphic-basics/%3Fprint%3D1&docid=OHI6Cigow5foxM&imgurl=http://fixbyproximity.com/wp-content/uploads/2011/07/square.png&w=500&h=500&ei=etDaTv3iDKKYiQKAzdWIDQ&zoom=1&iact=rc&dur=819&sig=114820397596981472587&page=1&tbnh=138&tbnw=184&start=0&ndsp=21&ved=1t:429,r:2,s:0&tx=59&ty=73
to this
http://images.google.com/imgres?q=rhombus&start=56&num=10&hl=en&safe=off&gbv=2&biw=1366&bih=667&tbm=isch&tbnid=IXv_701d24BJSM:&imgrefurl=http://www.fastgeometry.com/Encyclopedia/Polygons.htm&docid=kVsOTgeinbYEAM&imgurl=http://www.fastgeometry.com/images/rhombus.gif&w=155&h=195&ei=MdDaTv3FB8PXiQLv4PiICg&zoom=1&iact=hc&vpx=721&vpy=392&dur=3152&hovh=156&hovw=124&tx=90&ty=92&sig=114820397596981472587&sqi=2&page=4&tbnh=139&tbnw=111&ndsp=21&ved=1t:429,r:10,s:56
But yes, those are the functions I was referring to. They allow you to take a triangular portion of a picture and stretch it into any other shaped triangle, and by splitting your picture into two triangles you can make a square into a rhombus.
Last edited on Dec 4, 2011 at 1:47am
Dec 4, 2011 at 1:55am
Ah-ha. Yes, you want to shear.
Like I said, there are many ways to do this. With OpenGL, for example, it would look a lot like the GML code. You'd start drawing a polygon and you'd give vertices to the library.
It's also possible to transform a bitmap into another.
It all depends on what you have available and what exact results you expect.
Like I said, there are many ways to do this. With OpenGL, for example, it would look a lot like the GML code. You'd start drawing a polygon and you'd give vertices to the library.
It's also possible to transform a bitmap into another.
It all depends on what you have available and what exact results you expect.
Dec 4, 2011 at 2:50am
Is that shearing? I thought shearing was only with regular rotation.
In any case, thanks for your help!! I'll try OpenGL, sounds like it'll do the trick.
In any case, thanks for your help!! I'll try OpenGL, sounds like it'll do the trick.
Last edited on Dec 4, 2011 at 2:52am
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