Brief Instructions

On running, enter a filename as requested, or choose NEW if you are starting from scratch. If you have to change disks to load the screen image, make sure to replace the program disk so that the core program is loaded. This will run the main section. Once there, the following keys help you to use EDIT's features:

If you choose to Edit pixels by zooming in ('E') then the selected area to enlarge must be smaller than 29 by 39 pixels, and when in the editor, TAB toggles the pixel status from white to black or vice versa. Press COPY to save the result back to the clipboard and zoom back out.

At all times, watch for the prompt in the bottom left of the screen for details on what to do next.

EDIT - Remarks on v2.00
History

EDITCORE

EDIT

EDITENLARGED

EDIT

EDITCRE

EDITENL

EDIT

• Ensure output is to screen only, shift screen down because of my monitor, speed up the repeat rate and make the cursors do ASCII values so that you can't get that white square appearing in MODE7
• Menu chooses whether to go to PROCloadit or PROCnew
• Assemble the code, turn off error handling and goto the main program
• Assembler is commented as and when required, and integer variables (held even when CHAINing between programs) are set to important entry points. This means that if the code improved in the future, only "EDIT" would need to be updated and the other programs in the suite can make use of the new features
• PROCload gives the opportunity to put in your "Screen Images" disk or whatever or just press a key to skip past that prompt. If the file can't be found then the program is rerun. Otherwise Mode is changed and the file is loaded, irrespective of whether it is the right length, etc...
• PROCnew just changes MODE to black the screen and returns

EDITCRE

• Reset keyboard repeat rate in case EditENL altered it, and DIM some memory
• Enter main loop, poll the keyboard for some action. If it's a cursor key, then adjust the pointer's position accordingly. Depending on whether SHIFT was pressed the step rate is either *1 or *5 pixels at a time

  If the key pressed wasn't a cursor key, see if it was one of the keys that we're waiting for (by ANDing with &DF). CAPS can be on or off

• PROCmssg
  Reads from the bottom of the screen memory, keeping this safe in the buffer, and then types over the area with M$. The user is given 1 second to read this before the former screen is restored
• PROCcursor
  Draws a scaled-down box around the cursor. This routine is very simple as clipping is performed by the machine code, so no range checking needs to be done
• PROCframe
  Draws a border defined by the entry parameters by considering a box to be a set of 2 horizontal and 2 vertical lines
• PROCexpand
  Repeatedly calls PROCframe, keeping one set of coordinates constant and enlarging the other defined by which cursor key is pressed and the step defined by whether SHIFT was held down at the time. On receipt of a COPY, CHR$135, the values are ANDed with &FFFF so as only the bottom two bytes are ever checked by the M/C routines but BASIC allows four-byte integers. If the value has no depth or width, or none of either, then a message is flagged and you must give the box some size, at least 2*2 in size. Lastly, the coordinates are size ordered. This is essential because all other routines assume they are. This allows the box to be dragged from any corner and not just top-left down
• PROCdragframe
  Move the whole box around the screen by adding offsets to both the start and finish coordinates. Note that the box may be dragged off the screen; this is used mainly when pasting areas back from the clipboard. They can be cropped by the limits of the monitor
• PROCsaveselect
  This puts to a file only multiples of whole bytes to a file. This makes saving faster and easier
• PROCloadselect
  As a tradeoff of PROCsaveselect being simple, the reloading becomes more complex as not all of the bits in the file are needed. On entry X,Y,P,Q are copied as this is to be the destination, then the source X,Y,P,Q are restored by looking at the file. The routine cycles through one line at a time, first reading each row into a memory buffer then interpreting these values. The destination co-ordinate is calculated in X% and Y% is already set by the loop. A test is made to see if the pixel is on the screen or not (USR(T%) - test range). If it isn't then that is skipped to save time, and to stop the clipboard being pasted in two different places on the screen! If it was on the screen then the byte is read that refers to X%. Lastly, a bit comparison is made to see if the bit in the byte from the screen (data% from USR(G%) - get byte) matches that from the file buffer (?row%+some offsets). If they match, no action is required. Otherwise toggle the pixel to the correct value (CALL C% - calculate and write pixel)
• PROCclearselect
  Follows the same idea as PROCsaveselect but instead of filling the file with values read from the screen, it is filled with a pattern. 0 and 255 for black and white, or 170 for grey (binary 10101010). The renaming of the old clipboard file means that it is preserved, as the end user shouldn't know that when filling an area, they are in fact just loading a clipboard file in!
• FNditherbw
  Chooses the fill "colour"
• PROCtext
  Uses VDU5 and the OS's built-in character set to write text by Exclusive ORing. Delete function would not be possible unless the EOR option was used, as to delete the text you simply Exclusive OR a letter with itself
• PROCedit
  Checks the selection size and warns if it is too big. Otherwise, saves the current screen to "OUTPUT" and goes onto EDITENL
• FNscanclip
  Just tests the existance of a clipboard file, returning the handle

EDITENL

• Turns the cursor off again, as a Mode change restores it.
• Loads in the file by scanning through it serially and setting bytes in the screen to match the bit being scanned. The ! operator improves speed
• Once loaded, the cursor keys are set to return ASCII and TAB toggles the screen bytes by EORing with &FFFFFFFF. Again the ! operator is used
• Checks are made to ensure that the cursor hasn't moved beyond the bounds of the snippet. When done, the reverse process to loading is performed, i.e. the bit to put to file is determined by reading the screen memory
• It is the responsibilty of EDITENL to reload the main picture, as EDITCRE doesn't do this; to make the snippet paste itself the keyboard is stuffed with "P" using FX138

Robert Sprowson, EUG #33

Robert Sprowson