Transparency Tables

Look-up table for drawing a normal sprite using colour 0 as trasnparent.

C Usage

To use it in a C program, you have to define the constant cpct_transparentMaskTable00M0_address, selecting the location in memory where you want it to be, and include <sprites/transparency_tables.h>

// Include transparency table for mode 0 at 0x2100 (0x2100 - 0x21FF)
#define cpct_transparentMaskTable00M0_address 0x2100
#include <sprites/transparency_tables.h>

With this definition, you are including cpct_transparentMaskTable00M0 in your binary at address 0x2100 (256-bytes aligned, from 0x2100 to 0x21FF, never changing the Most significant byte).  You are always required to provide a concrete address for this table at definition time.

General recommendations

• Be vigilant with the use of explicit addresses in SDCC.  It is recommended that you group together all explicitly located items in one single file.  Otherwise, memory locations may be messed up in the final binary by the linker.
• Remember that locating items at a specific memory location is done writing them at a concrete location in the final binary, taking into account where it will be loaded.  That can make the size of the final binary increase, and even overwrite parts of the memory you did not intended.  For instance, imagine you have a binary with 1024 (0x400) bytes of code that you load at memory address 0x1000.  That binary occupies memory from 0x1000 to 0x1400 when loaded.  If you try to explicitly place the transparent table at location 0x8000 in memory, what the compiler does is creating a 28K binary, with code at first 1024 (0x400) bytes, 27K of zeros (from 0x1400 to 0x8000) and then 256 (0x100) bytes with the table.  That could erase unintended things in memory when loading.
• Always do your own calculations to prevent explicitly placing things overlapped.  It is recommended that you put your explicitly located data items first, previous to the starting memory address of your program.  That’s easier to manage.

Size

256 (0x100) bytes

Details

Look-up table (array) containing all the masks for the 256 possible combinations of byte pixel data values, assuming firmware colour 0 as being transparent.  It is used by sprite-drawing functions to draw the sprites using colour 0 as transparent.

This table should be placed at a specific location in memory.  It is recommended to place it at a 256-byte aligned memory location (a memory location whose Least signficant byte is 0, so the address has the form 0x??00).  In fact, some functions like cpct_drawSpriteMaskedAlignedTable require it to be 256-byte aligned or they will fail.

To be able to use this table, all you have to do is defining the macro (constant value) cpct_transparentMaskTable00M0_address before the inclusion of <sprites/transparency_tables.h>, CPCtelera’s header file.

Once the table has been defined, you can access it through the symbol cpct_transparentMaskTable00M0.