BMP manipulations

[Norm Shupe]

A topographic map tile, containing a specified Latitude and Longitude, is to be located at the center of a 5 by 5 array of geographically contiguous map tiles. The array of map tiles are shown below where the central map tile containing the specified coordinate set is at position B12:

B00 B01 B02 B03 B04
B05 B06 B07 B08 B09
B10 B11 B12 B13 B14
B15 B16 B17 B18 B19
B20 B21 B22 B23 B24

The individual map tiles are in a BMP-compatible format, with a common 256 color LUT and each containing 256 x 256 pixels for a total of 66,614 bytes including the standard 1078 byte header for a 256 color LUT. It is desired to assemble this 25 tile array into a single BMP compatible file containing 1280 x 1280 pixels. The size of the file would then be 1,639,478 bytes including the 1078 byte header.

The PB code I have used to accomplish this process is shown below. The implementation works correctly but is slower than i would prefer. Could anyone suggest an approach that would be faster than reading each tile into a temporary array (TileArray) and then loading, pixel by pixel, the TileArray contents into the desired location in the 1280 x1280 array (CompositeArray)??

REGISTER Column AS LONG
REGISTER Row AS LONG
DIM RowNumber AS LONG
DIM RowIndex AS LONG
DIM IndexRow AS LONG
DIM ColumnIndex AS LONG
DIM N AS LONG
DIM BMPCount AS LONG
DIM BMPArray(1 TO 66614)AS BYTE
DIM CompositeArray(1 TO 1639478)AS BYTE

FOR BMPCount = 0 TO 24

OPEN "C:\Tile(" & BMPCount & ").bmp" FOR BINARY ACCESS READ AS 1
GET 1, 1, BMPArray()
CLOSE 1

If BMPCount=0 then
FOR N = 1 TO 1078
CompositeArray(N) = BMPArray(N) 'LOAD THE HEADER
NEXT N
END IF

RowIndex = (BMPCount \ 5) * 327680
ColumnIndex = 1079 + (BMPCount MOD 5) * 256

FOR Row = 0 TO 255
IndexRow = Row * 256
RowNumber = RowIndex + IndexRow * 5

FOR Column = 0 TO 255
CompositeArray(ColumnIndex + Column + RowNumber) = BMPArray(1079 + Column + IndexRow)
NEXT Column

NEXT Row

NEXT BMPCount

OPEN C"C:\Composite.bmp" FOR BINARY ACCESS WRITE AS 1
PUT 1, 1, CompositeArray()
CLOSE 1

[Paul Dixon]

Norm,
if you calculate the start address of each 256 byte row of your small bitmap using VARPTR(BMParray(row,col)) and calculate the location in the big bitmap to which that row must be copied then you can use PEEK$ and POKE$ to copy 256 bytes at a time.


Your arrays look small enough that they shouldn't take a lot of time even your way. How long does this process take and how much faster do you need it to be? I'd guess that the time taken to read the data from disk and write the result back will be a lot longer than the time taken to manipulate that data.

Paul.

[Norm Shupe]

Thanks for the suggestion Paul. On my machine, the entire process takes about 300 ms and I was hoping to get more like 30 ms. This process is being executed as part of a DLL interfaced to a VB6 application. Unfortunately, the target machine is quite a bit slower than my development machine. I will take a shot at your suggestion when I return from Virginia this weekend.

[Chris Holbrook]

You could use peek/poke$ or movememory (see API), also you can use bitwise shifts instead of multiplication (not sure if Powerbasic might do this for you?)

Both of these in several places.

Best to use code highlighting (hash symbol in message editor) to save eyes - mine that is.