4 ms·

No, they’re equivalent. Nobody stops you from from stepping through pixels in multiples of 4 and then writing that to the display buffer.

ajuc 6y ago
You can write code both ways but it's much easier to ensure every destination pixel is handled exactly once when you interate over the destination pixels, than if you do it iterating over the source pixels. It becomes especially visible when you add perspective distortion and other complications. Which is why every graphic api out there does it pull-style.
- heavenlyblue 6y ago
  Drawing triangles on a screen is a push-style operation, isn’t it?
  - ajuc 6y ago
    Yes, from the POV of lists of polygons. But from the point view of textures it is pull (you go through destination pixels and fill them with source pixels fetched through transformation).
    - heavenlyblue 6y ago
      In the same way you could apply the reverse transform to the polygon and get the coordinates of display pixels in texture coordinates and then do a push from there. They are equivalent, as I am trying to say. The only difference is semantics or whatever makes it easier to think about.
      - ajuc 6y ago
        You would have to skip variable number of pixels in source texture according to the transformation, then calculate the reverse transformation to know where to push. Notice how you not only change x * 4 into x/4, you also change x++ into x+=4 for (int x=0; x<width; x++) for (int y=0; y<height; y++) destination[x][y] = source[x*4][y*4]; vs for (int x=0; x<width; x+=4) for (int y=0; y<height; y+=4) destination[x/4][y/4] = source[x][y]; If it's as simple as scaling: x+=4 isn't much harder than x++. But for complex transformations calculation of how many pixels to skip in any particular row will be slow and complicated. Meanwhile when doing pull you don't need to do it. This is the reason every graphical API i know of does these tranformations iterating over destination pixels.
hoseja 6y ago
Also, what if you want to use a better scaling method.
chrisbennet 6y ago
Yes, you are of course correct for this very simple example. The last time I did something like this, I needed to take a rectangular buffer and transform it to a circle. Each buffer line became a "spoke" in the circle. Much easier/simpler [I always strive for simple] to figure out the reverse transform and step through every "display" pixel.

ajuc 6y ago

You can write code both ways but it's much easier to ensure every destination pixel is handled exactly once when you interate over the destination pixels, than if you do it iterating over the source pixels. It becomes especially visible when you add perspective distortion and other complications. Which is why every graphic api out there does it pull-style.

heavenlyblue 6y ago
Drawing triangles on a screen is a push-style operation, isn’t it?
- ajuc 6y ago
  Yes, from the POV of lists of polygons. But from the point view of textures it is pull (you go through destination pixels and fill them with source pixels fetched through transformation).
  - heavenlyblue 6y ago
    In the same way you could apply the reverse transform to the polygon and get the coordinates of display pixels in texture coordinates and then do a push from there. They are equivalent, as I am trying to say. The only difference is semantics or whatever makes it easier to think about.
    - ajuc 6y ago
      You would have to skip variable number of pixels in source texture according to the transformation, then calculate the reverse transformation to know where to push. Notice how you not only change x * 4 into x/4, you also change x++ into x+=4 for (int x=0; x<width; x++) for (int y=0; y<height; y++) destination[x][y] = source[x*4][y*4]; vs for (int x=0; x<width; x+=4) for (int y=0; y<height; y+=4) destination[x/4][y/4] = source[x][y]; If it's as simple as scaling: x+=4 isn't much harder than x++. But for complex transformations calculation of how many pixels to skip in any particular row will be slow and complicated. Meanwhile when doing pull you don't need to do it. This is the reason every graphical API i know of does these tranformations iterating over destination pixels.

hoseja 6y ago

Also, what if you want to use a better scaling method.

chrisbennet 6y ago

Yes, you are of course correct for this very simple example. The last time I did something like this, I needed to take a rectangular buffer and transform it to a circle. Each buffer line became a "spoke" in the circle. Much easier/simpler [I always strive for simple] to figure out the reverse transform and step through every "display" pixel.