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111 lines
2.8 KiB
Markdown
111 lines
2.8 KiB
Markdown
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[← Home](../README.md) · [Graphics](README.md)
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# Animation — GEL System: BOBs, VSprites, AnimObs
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## Overview
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The **GEL (Graphics ELement)** system provides high-level animated sprite and bitmap overlay support. It manages VSprites (virtual sprites that can use hardware or software rendering), BOBs (Blitter OBjects — arbitrary-sized bitmaps overlaid on a playfield), and AnimObs (animation objects with sequencing).
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---
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## VSprite
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```c
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/* graphics/gels.h — NDK39 */
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struct VSprite {
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struct VSprite *NextVSprite;
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struct VSprite *PrevVSprite;
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struct VSprite *DrawPath;
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struct VSprite *ClearPath;
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WORD OldY, OldX; /* previous position */
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WORD Flags; /* VSPRITE, SAVEBACK, OVERLAY, MUSTDRAW */
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WORD Y, X; /* current position */
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WORD Height;
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WORD Width; /* width in words */
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WORD Depth;
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WORD MeMask; /* collision mask */
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WORD HitMask;
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WORD *ImageData; /* sprite image */
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WORD *BorderLine; /* collision border */
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WORD *CollMask; /* collision mask data */
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WORD *SprColors; /* colour table */
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struct Bob *VSBob; /* if this VSprite backs a BOB */
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BYTE PlanePick;
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BYTE PlaneOnOff;
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/* ... */
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};
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```
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---
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## BOB (Blitter Object)
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```c
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struct Bob {
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WORD Flags;
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WORD *SaveBuffer; /* background save buffer */
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WORD *ImageShadow; /* shadow mask for cookie-cut */
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struct Bob *Before;
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struct Bob *After;
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struct VSprite *BobVSprite; /* associated VSprite */
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struct AnimComp *BobComp; /* if part of animation */
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struct DBufPacket *DBuffer; /* double-buffer packet */
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};
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```
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---
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## Usage Pattern
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```c
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struct GelsInfo gi;
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struct VSprite headVS, tailVS;
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/* Initialise GEL system: */
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InitGels(&headVS, &tailVS, &gi);
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rp->GelsInfo = &gi;
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/* Add a VSprite/BOB: */
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AddVSprite(&myVSprite, rp);
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/* or */
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AddBob(&myBob, rp);
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/* Each frame: */
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SortGList(rp); /* sort by Y position */
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DrawGList(rp, &vp); /* render all GELs */
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WaitTOF(); /* sync to vertical blank */
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/* Cleanup: */
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RemVSprite(&myVSprite);
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/* or */
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RemBob(&myBob);
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```
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---
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## AnimOb — Animation Sequences
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```c
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struct AnimOb {
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struct AnimOb *NextOb;
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struct AnimOb *PrevOb;
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LONG Clock; /* frame counter */
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WORD AnOldY, AnOldX;
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WORD AnY, AnX; /* current position */
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WORD YVel, XVel; /* velocity */
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WORD YAccel, XAccel; /* acceleration */
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WORD RingYTrans; /* ring buffer Y translation */
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WORD RingXTrans;
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struct AnimComp *HeadComp; /* component chain */
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/* ... */
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};
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```
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---
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## References
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- NDK39: `graphics/gels.h`, `graphics/gelsinternal.h`
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- ADCD 2.1: `InitGels`, `AddVSprite`, `AddBob`, `SortGList`, `DrawGList`
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- *Amiga ROM Kernel Reference Manual: Libraries* — GELs chapter
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