BitMapScale
sonountalebanJunior Member
Posted 2 months agoHello,
I'm trying to use BitMapScale for my porting of System Shock and it doesn't look right what I got...
It seems it shows just the channel blue, discarding the red and the green. There is a lack of documentation of this function (by the way is it a genuine AmigaOS 3.1 function?) and the only one example I found for AROS didn't help me much.
The source bitmap has been created using AllocBitMap with these flags (BMF_CLEAR | BMF_INTERLEAVED | BMF_MINPLANES) and no "friend bitmap", while the dest bitmap is the one associated with the RastPort of the main window. All have 8 as depth.
I'm trying to use BitMapScale for my porting of System Shock and it doesn't look right what I got...
It seems it shows just the channel blue, discarding the red and the green. There is a lack of documentation of this function (by the way is it a genuine AmigaOS 3.1 function?) and the only one example I found for AROS didn't help me much.
Code Download source
struct BitScaleArgs bms_args;
bms_args.bsa_SrcBitMap = pMainScreenRastPort->BitMap;
bms_args.bsa_DestBitMap = pMainRastPort->BitMap;
bms_args.bsa_Flags = 0;
bms_args.bsa_SrcWidth = gWindowWidth;
bms_args.bsa_SrcHeight = gWindowHeight;
bms_args.bsa_SrcX = 0;
bms_args.bsa_SrcY = 0;
bms_args.bsa_DestX = 0;
bms_args.bsa_DestY = 0;
bms_args.bsa_XSrcFactor = gWindowWidth;
bms_args.bsa_XDestFactor = gScreenWidth;
bms_args.bsa_YSrcFactor = gWindowHeight;
bms_args.bsa_YDestFactor = gScreenHeight;
BitMapScale(&bms_args);
The source bitmap has been created using AllocBitMap with these flags (BMF_CLEAR | BMF_INTERLEAVED | BMF_MINPLANES) and no "friend bitmap", while the dest bitmap is the one associated with the RastPort of the main window. All have 8 as depth.
Edited by sonountaleban on 25-01-2026 06:17, 2 months ago
sonountalebanJunior Member
Posted 2 months agosonountalebanJunior Member
Posted 2 months agoI found the palette is ok, if I call after it shows correctly the original bitmap over the scaled version.
Code Download source
ClipBlit(pMainScreenRastPort, 0, 0, pMainRastPort, 0, 0, gScreenWidth, gScreenHeight, 0xc0);Code Download source
BitMapScale(&bms_args);deadwoodAROS Dev
Posted 2 months agoHere is a suggestion from another developer:
Use 3 bitmaps. Your original game bitmap(A), bitmap identical to you game bitmap but with the size of the screen(
and screen bitmap (C). BitMapScale from A to B, then then Blit from B to C. Essentially disconnect steps of scalling and blitting to screen.
Use 3 bitmaps. Your original game bitmap(A), bitmap identical to you game bitmap but with the size of the screen(
and screen bitmap (C). BitMapScale from A to B, then then Blit from B to C. Essentially disconnect steps of scalling and blitting to screen.1 user reacted to this post
sonountaleban
sonountalebanJunior Member
Posted 2 months ago@deadwood - Here is a suggestion from another developer:
Use 3 bitmaps. Your original game bitmap(A), bitmap identical to you game bitmap but with the size of the screen(B) and screen bitmap (C). BitMapScale from A to B, then then Blit from B to C. Essentially disconnect steps of scalling and blitting to screen.
Thank you, now it's better. :)
However, while vertical scaling is absolutely fine, horizontally is buggy until XDestFactor is equal to XSrcFactor...
My code now looks like this:
Code Download source
bms_args.bsa_SrcBitMap = pMainScreenRastPort->BitMap;
bms_args.bsa_DestBitMap = pScaledMainScreenRastPort->BitMap;
bms_args.bsa_Flags = 0;
bms_args.bsa_SrcWidth = gWindowWidth;
bms_args.bsa_SrcHeight = gWindowHeight;
bms_args.bsa_SrcX = 0;
bms_args.bsa_SrcY = 0;
bms_args.bsa_DestX = 0;
bms_args.bsa_DestY = 0;
bms_args.bsa_XSrcFactor = gWindowWidth;
bms_args.bsa_XDestFactor = gScreenWidth;
bms_args.bsa_YSrcFactor = gWindowHeight;
bms_args.bsa_YDestFactor = gScreenHeight;
BitMapScale(&bms_args);
BltBitMapRastPort(pScaledMainScreenRastPort->BitMap, 0, 0, pMainRastPort, 0, 0, gScreenWidth, gScreenHeight, 0xc0);
sonountalebanJunior Member
Posted 2 months agosonountalebanJunior Member
Posted 2 months agoEdited by sonountaleban on 26-01-2026 15:11, 2 months ago
sonountalebanJunior Member
Posted 2 months agosonountalebanJunior Member
Posted 2 months agoSorry, I did a mess with the posts here... Anyway, I've copied the newer graphics.library into my hosted AROS installation and I got a bit different result:
2 users reacted to this post
aha, Argo
deadwoodAROS Dev
Posted 2 months agosonountalebanJunior Member
Posted 2 months agoFixed... I needed to make the off screen bitmap "friend" of the main window bitmap. Also I have to use WriteChunkyPixels now, because my C2P routine stopped to work in hosted mode (release executable) and with AxRuntime (debug executable). However, I had tried to make it friend before the updated bitmapscale.c file and it didn't work.
I've noticed the low-res is much slower in hosted mode, while under AxRuntime or running in a native AROS installation it's the fastest resolution as expected.
This is the biggest res (1024x768) and on my machine it runs at similar frame rates in every environment.
I forgot a thing, I've removed the intermediate buffer for BitMapScale, it works well dealing directly with the window bitmap and the offscreen bitmap.
I've noticed the low-res is much slower in hosted mode, while under AxRuntime or running in a native AROS installation it's the fastest resolution as expected.
This is the biggest res (1024x768) and on my machine it runs at similar frame rates in every environment.
I forgot a thing, I've removed the intermediate buffer for BitMapScale, it works well dealing directly with the window bitmap and the offscreen bitmap.
Edited by sonountaleban on 27-01-2026 21:00, 2 months ago
3 users reacted to this post
aha, Argo, Farox
sonountalebanJunior Member
Posted 2 months agoEdited by sonountaleban on 28-01-2026 05:57, 2 months ago
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