; Copyright 1996 Acorn Computers Ltd
;
; Licensed under the Apache License, Version 2.0 (the "License");
; you may not use this file except in compliance with the License.
; You may obtain a copy of the License at
;
; http://www.apache.org/licenses/LICENSE-2.0
;
; Unless required by applicable law or agreed to in writing, software
; distributed under the License is distributed on an "AS IS" BASIS,
; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
; See the License for the specific language governing permissions and
; limitations under the License.
;
; Sources.JPEG
; 14th September 1993 WRS - started
; 1st November 1993 WRS - modified to simplify memory allocation interface
; Some parts of JPEG decoding are done in C, code in Sources.PutScaled
; provides assistance for debugging output.
[ jpeg
; ----------------------------------------------------------------------
; R1->sprite
; Preserve all registers
; Need to set up, for entry into the C code:
; static int jpeg_scan_file(
; decompress_info_ptr cinfo, in r0
; char *file_image, r1
; int image_length, r2
; int xmin, r3
; int xmax, [sp,#0]
; int width, [sp,#4]
; int height, [sp,#6]
; BOOL dc_only); [sp,#8]
; lr = wp value from the assembler
; On exit the stack arguments will have been removed for us.
;jpeg_scan
; Push "R0-R12,LR"
; ; get ready to call C code
; MOV SL,R12 ; will be left alone by compiled C - for debug routines above.
; ADRL R3,ccompiler_sp
; ADD R2,SP,#4*14 ; calling SP value
; STR R2,[R3] ; in case of unexpected exit
; ; R1 = sprite
; ; set up the fetchroutine, for use by any subsequent compiled code.
; ADR R2,jpeg_fetchroutine
; STR R2,fetchroutine
; ; set up the band buffer pointer and size in the jpeg workspace:
; ; see h.jpegdata for details of the workspace layout,
; MOV R4,R1 ; keep sprite pointer - R0-R3 trashed by calling C code
; BL jpeg_workspace_size ; call C: R0 = size needed in bytes
; MOV R12,SL ; R12 is ip to a C prog, will have been trampled on - restore it.
; ADRL R1,jpeg_space ; base of workspace - a decompress_info_struct
; ADD R0,R0,R1 ; R0 = spare space - the band buffer
; ADRL R2,jpeg_band_buffer
; STR R0,[R2] ; store band buffer pointer
; ADRL R2,jpeg_end
; SUB R0,R2,R0 ; band buffer size in bytes
; MOV R0,R0,LSR #2 ; size in words
; BIC R0,R0,#15 ; round down to multiple of 16
; ADRL R2,jpeg_band_buffer_size
; STR R0,[R2] ; store band buffer size
; MOV R1,R4 ; keep hold of sprite pointer
; STR R1,save_sprite
; Pull "R0-R12,PC"
; ----------------------------------------------------------------------
jpeg_fetchroutine
; This is called every line by compiled code from PutSpriteScaled, when the
; source is JPEG compressed data.
; Entry:
; r0 = y coordinate
; r12 = wp
; Exit:
; r0 = initial address to get RGB data from for this line, based on wp->in_x and given y coord.
; all other registers preserved.
; This works by calling the C proc jpeg_find_line, defined in h.rojpeg, as:
; static int *jpeg_find_line(decompress_info_ptr cinfo, int ycoord);
Push "R1-R3,R10-R12,LR" ; r4-r9 are preserved by C code.
MOV R1,R0 ; arg2 - int y coord
ADRL R0,jpeg_space ; arg1 - decompress_info_ptr cinfo
; get ready to call C code
MOV SL,R12 ; will be left alone by compiled C - for debug routines above.
; and call
BL jpeg_find_line ; base of that line in R0 on return
MOV R12,SL ; R12 is ip to a C prog, will have been trampled on - restore it.
; returned value is int* for base of line.
; now add in the initial source X coordinate.
LDR R1,in_x ; x offset, as word count
;Debug cc,"x offset to add",R1
ADD R0,R0,R1,LSL #2 ; add word offset
Pull "R1-R3,R10-R12,PC" ; restore registers and return to compiled code.
]
END