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# SDL zoom (source bigger than the screen)

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6 replies to this topic

### #1Ultimate_Fusion  Members

Posted 02 March 2007 - 09:30 AM

What I want to do? zoom in and out a large surface (bigger than the screen,1000 by 700) What I have done so far! I am using SDL's rotozoom.I have managed to rotate and zoom (I only need the zoom) the screen. The problem! the "playing" surface is bigger than the screen so zooming the current screen is just zooming the top left of the whole playing area. I need to be able to zoom the whole "playing" surface from what i under stand you can only blit surfaces to the screen. like SDL_BlitSurface(spriteSurface,sprite source, screenSurface, screen dest ) and zooming each surface wont make the positions proportional and i have a repeated background and a lot of sprites on the screen. so how can I either: blit surfaces to another bigger surface or using a larger surface than the screen to blit to?

### #2samuraicrow  Members

Posted 02 March 2007 - 02:20 PM

SDL_BlitSurface will blit to a larger surface if you like. It is only if you are using OpenGL that you can blit only to the screen (and OpenGL will do scaling for you if you know how to do it). Using a wrapper for OpenGL such as hxRender will be helpful if you want to zoom each sprite as you plot it but it may have speed drawbacks if you are using sprites/tiles that aren't an even power of 2 (...8,16,32,64,128,256 or 512), or are larger than 512 pixels.

The only unfortunate part about using rotozoom is that it is a software-only zoom function. You can probably make a faster one on your own by leaving out the rotation functionality out but you may lose detail if you do it the way I am thinking.

### #3Ultimate_Fusion  Members

Posted 03 March 2007 - 03:02 AM

my sprites are a multiple of 2.
I have tried hxRender and it is too slow.

how do blit a surface to another surface that isn't the screen.

I tried it the usual way and it didn't work.

also behind the rotozoom surface is a black background. when I move the rotozoom surface left or right it leaves a blurd effect. there is nothing on this black background and updating the screen doesn't fix this

### #4samuraicrow  Members

Posted 03 March 2007 - 05:03 AM

SDL_CreateRGBSurface will create a larger than life surface for you. Only make sure it is the same color-depth as your sprites.

As for hxRender being too slow, it has to be an even POWER of 2 not just a multiple of 2. Otherwise it splits the image up into multiple blits. If you use one of the sizes I listed above it would be faster.

As for the rotozoom function, I wouldn't use it if you are trying to animate in realtime. Try this (in psuedo C code):
for(y=destMaxY ; y>=0 ; y--){  for(x=destMaxX ; x>=0 ; x--)  {    PutPixel( destScreen, x,y, GetPixel(srcSurface, x*srcSurfaceMaxX/destMaxX, y*srcSurfaceMaxY/destMaxY);  }}

You'll lose detail because the spaces in between the pixels in the source won't be mixed together to make the destination color but it will be fast.

### #5Ultimate_Fusion  Members

Posted 03 March 2007 - 07:23 AM

my picture is 64 by 64 bit. my background image zomms and moves fine but when I add my charcter class to the main process it slows it down 10 fold. It is about 200-300 lines of code.

for(y=destMaxY ; y>=0 ; y--){  for(x=destMaxX ; x>=0 ; x--)  {    PutPixel( destScreen, x,y, GetPixel(srcSurface, x*srcSurfaceMaxX/destMaxX, y*srcSurfaceMaxY/destMaxY);  }}

from the code above is
srcSurfaceMaxX - the width of the screen or the sprite
and what is destMaxy?

### #6samuraicrow  Members

Posted 03 March 2007 - 12:17 PM

srcSurfaceMaxX is the maximum x coordinate of the source surface and srcSurfaceMaxY is the maximum y coordinate of the source surface. destMaxX is the maximum x coordinate of the destinateion surface (the screen) and destMaxY is the maximum y coordinate of the destination surface.

The psuedo-code I listed will scale a bitmap down to the size of the destination surface/screen.

-edit-
By the way. Have you figured out that you can blit from surface to surface yet? (As long as you are just using SDL and not hxRender you can create a surface with SDL_CreateRGBSurface, that is)

### #7Ultimate_Fusion  Members

Posted 04 March 2007 - 05:16 AM

yeah i got SDL_CreateRGBSurface to work and it is running abit faster.

so far I
create a sprite
put that sprite on the SDL_CreateRGBSurface
zoom the SDL_CreateRGBSurface surface

your psuedo-code looks like it zoom each sprite separatley.
i zoom the whole image. i am guessing this will be alot slower?
how who the psuedo-code change for just zooming the whole SDL_CreateRGBSurface surface?

cheers

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