First commit of something actually working, at least with my demo file.

Makefile

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+SOURCES_DIR=./src
+BUILD_DIR=./build
+DIST_DIR=./dist
+RSC_DIR=./rsc
+
+CC=m68k-atari-mint-gcc
+CFLAGS=-c -O3
+LINKFLAGS=-lz -s -Wl,--gc-sections
+
+# VASM PARAMETERS
+ASM=vasmm68k_mot
+ASMFLAGS=-Faout -quiet -x -m68000 -spaces -showopt
+
+all: prepare dist
+
+prepare:
+	mkdir -p $(BUILD_DIR)
+
+clean-compile : clean buffer.o screen.o main.o
+
+sndhisr.o: prepare
+	$(ASM) $(ASMFLAGS) $(SOURCES_DIR)/sndhisr.s -o $(BUILD_DIR)/sndhisr.o
+
+sndh.o: prepare
+	$(CC) $(CFLAGS) $(SOURCES_DIR)/sndh.c -o $(BUILD_DIR)/sndh.o
+
+stvn.o: prepare
+	$(CC) $(CFLAGS) $(SOURCES_DIR)/stvn.c -o $(BUILD_DIR)/stvn.o
+
+line.o: prepare
+	$(CC) $(CFLAGS) $(SOURCES_DIR)/line.c -o $(BUILD_DIR)/line.o
+
+main: stvn.o line.o sndh.o sndhisr.o
+	$(CC) \
+	      $(BUILD_DIR)/*.o \
+		  -o $(BUILD_DIR)/stvn.prg $(LINKFLAGS);
+
+dist: main
+	mkdir -p $(DIST_DIR)
+	cp $(BUILD_DIR)/stvn.prg $(DIST_DIR)
+	m68k-atari-mint-strip -s $(DIST_DIR)/stvn.prg
+	cp -R $(RSC_DIR)/* $(DIST_DIR)
+
+clean:
+	rm -rf $(BUILD_DIR)
+	rm -rf $(DIST_DIR)
+

README.md

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+# STVN
+A very simple visual novel engine for Atari ST on monochrome high-res mode.
+
+![stvn](/assets/stvn.png)
+
+## Building
+To build this, you need the following:
+* GNU make
+* m68k-atari-mint gcc toolchain
+* vasmm68k_mot
+
+## Prerequistes
+* Atari ST (STe if you want to use DMA SNDH files)
+* 1024KiB RAM, since mintlib refuses to init on 512K models. Everyone have 4MiB nowadays, right?
+* Any TOS version should work (tested only on TOS 2.06)
+
+## Running
+* Provide a script file following the documented syntax
+* Edit STVN.INI to meet your needs: script file and SNDH memory buffer, which should be the size of your largest SNDH file
+* Run STVN.PRG from GEM Desktop.
+
+## Key bindings
+* 'Space' to advance
+* 'q' Quit
+* 's' Save state
+* 'l' Load state
+* 'b' Go back 1 text block
+* 'h' Show help screen
+
+## STVN.INI settings
+As a sample, use the following:
+```
+STEST.VNS
+B20000
+```
+'S' line is the script file
+'B' line is the SNDH buffer space
+Defaults: ``STVN.VNS`` & ``20000``
+
+## Supported formats / limitations:
+* For pictures: PI1/PI3 monochrome, uncompressed 32KiB files.
+  The palette isn't used, only the first 25600 bytes are read (640x360 image, leaving 40 pixels for text, 4 lines)
+
+For audio: any SNDH with a working playback routine compatible with gwEm's sndhlib
+Both can be gzipped.
+
+Savestates: 4 supported, adding more would be trivial.
+10 VN choices binary "registers", adding more wouldn't be very hard.
+Scripts can be 999999 lines long.
+
+All resource files must be placed in the 'data' subdirectory.
+
+## Syntax:
+Each line starts with an operand, like:
+``IATARI.PI3``
+
+Supported operands:
+* 'W' : Wait for input
+
+  This is where most interaction will happen.
+
+  Like saving/loading, waiting for 'space', quitting, etc...
+
+* 'I' : Change background image
+
+  Syntax: ``I[file]`` like ``IFILE.PI3``
+
+  Expected format is PI3, can (should) be gzipped, and is loaded entirely before being copied to video memory.
+
+  Only the first 320 lines are loaded and drawn, the rest of the screen being used for the text area.
+
+  A few bytes can thus be saved, for example bv removing the 400-lines padding code in pbmtopi3 source.
+
+  As the picture is loaded in RAM before being copied in vram, this operand will use 32000 bytes of RAM during operation, freed after.
+
+  This will obviously erase all sprites and clear the internal sprite list.
+
+* 'S' : Sayer change
+
+  Syntax: ``Sname`` like `SToyoyo`
+
+  Obviously, this will reset character lines to 0.
+
+  This is used as the save pointer and will also reset the text box.
+
+* 'T' : Text line
+
+  Syntax: ``Ttext`` like ``THere's a text line``
+
+  Line wrapping is disabled, so make sure a line isn't more than 79 characters!
+
+* 'P' : Change music
+
+  Syntax: ``P[file]`` like ``PFILE.SND``
+
+  Expected format is uncompressed SNDH (use unice68), but can and should be gzipped, and is loaded entirely before starting its playing routine.
+
+  This uses gwEm's sndhlib code, which should be pretty robust, but I'm not responsible for bugged replay routines in SNDH files...
+
+  Note: Be sure to adjust the 'B' Line in STVN.INI to match the *uncompressed* size of your largest tune. The default is 20000 bytes.
+
+* 'J' : Jump to label
+
+  Syntax: ``J[label]`` like `JLBL1```
+
+  A label 4 bytes sequence at the beginning of a line
+
+* 'C' : Offer a choice and store it in a register
+
+  Key '1' entered: store 0
+
+  Key '2' entered: store 1
+
+  Syntax: ``C[register number]`` like ``C0``
+
+  Also offer the same interactions as a 'W' line.
+
+* 'R' : Redraw the background picture.
+
+  More precisely, copy back the buffer of last loaded one into video memory.
+
+  This will obviously erase all sprites and clear the internal sprite list.
+
+* 'B' : Jump to label if register is set.
+
+  Syntax: ``B[register number][label]`` like ``B0LBL1``
+
+* 'D' : Wait the specified number of milliseconds (max 99999).
+
+  Syntax: ``D[msec]`` like ``D2000``
+
+* 'A' : Load and draw a sprite in video memory.
+
+  Syntax: ``A[XXX][YYY][file]`` like ``A000000TOYO.SPR``
+
+  The expected format is derived from XPM, can (should) be gzipped and is plotted as it's read.
+
+  A converter script is provided.
+
+  Screen boundary are checked during drawing, but you can draw on the text area if you want.
+
+  More precicely: X coordinates after 640 are ignored and Y coordinates after 400 ends the drawing routine.
+
+  This can use quite some memory: 1 byte per pixel, allocated in 1024 bytes blocks, freed after operation.
+
+  And this is still drawn slower than a full screen image.
+
+  They're tracked as much as I could during load & back routines, so what *should* happen is:
+
+  * If you load a save, both background & sprites ('A' lines) encoutered between the lasts 'I' or 'R' lines are drawn.
+  * If you go back and neither background & sprites changes: nothing is drawn
+  * If you go back and there's a background change, this will also trigger a sprite draw pass.
+  * If you go back to the 'S' line just before a 'A' Line, it will trigger a draw pass too. This is by design: When the 'S' line happens, the sprite doesn't exist yet.

demo/stdemo.vns

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+PTEST.SNZ
+ISTREET.PIZ
+SHinata
+TI love taking nighttime strolls!
+TI usually walk until down.
+TI might be a night owl...
+TOr, maybe it's just I like walking.
+W
+SHinata
+TI want to write many lines today.
+TOh, what happened?
+TDid it clear the text box?
+TYes it did!
+A100000HINA.SPZ
+W
+SHinata
+TWhat do I do?
+T1:Stay?
+T2:Leave?
+C0
+B0LSC2
+SKana
+TI want to say something too!
+A500000HINA.SPZ
+W
+SHinata
+TWhat I was saying again? And my line count even went back to 0...
+W
+SHinata
+TAnyway...
+W
+LSC2
+Pcubase.snd
+ISTREET01.PI3
+SHinata
+TLet's just go out, which resets it again.
+TSeems the music is different, too?
+W
+SHinata
+TAnd well, it feels better.
+T\o/
+W
+SHinata
+TA last line before I go.
+W
+Psos.snd
+IHOUSE.PI3
+SHinata
+TTadaima!
+TThat's nice.
+A200000HINA.SPZ
+W
+B0LSC3
+SHinata
+TBut I'll need to quit soon.
+W
+SHinata
+TSadly
+W
+JLSC4
+LSC3
+SHinata
+TOk!
+W
+SHinata
+TI'll watch a movie.
+W
+SHinata
+TThen take a nap.
+W
+LSC4
+

demo/xpmtospr.sh

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+#!/bin/bash
+
+[ "$1" == "" ] && echo "Usage: $(basename $0) [xpm file]" && exit 1
+tail -n +7 "$1" | sed 's/"//g' | sed 's/,//g' | sed 's/}//g' | sed 's/;//g' | sed 's/"//g' | sed 's/+/0/g' | sed 's/\./1/g'

rsc/stvn.ini

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+SSTDEMO.VNS
+B20000