First steps into a more "colorful" emulation

One of the major features of phase #2, as we originally wrote in the milestone and phase plan two years ago, is adding support for Color QuickDraw emulation. Even though a lot of APIs considered part of phase #1 are still incomplete, the application compatibility and overall progress of project appears good enough to justify starting the work on that particular feature at this point. Nevertheless, all missing phase #1 features will be worked on simultaneously as they come up when testing the applications.

Adding color support will eventually allow us to test a huge number of new applications and games, and it will also allow trying out the existing ones in color modes. Especially games from the early 1990s have very good support for multiple color depths, so it should be interesting (for example, Civilization’s support for 1-bit and 256 colors, Railroad Tycoon’s 1-bit and 16 color support, Glider’s 16-color art, etc…)

First steps: The slot-based architecture

Originally Apple’s Mac II lineup had a quite different architecture from the old “classic”-type compact macs, which also reflects on how Color QuickDraw operates. Instead of dividing the memory space into four regions as in “classic” Macs (4mb RAM, 4mb ROM, 4mb I/O and 4mb VIA space), the slot-based models (in original 24-bit model) divide memory into 1mb “slots”, which are more dynamically assigned. For example, IM:Memory 3-6 describes the following model (in 24-bit mode):

  • 0x000000-0x7FFFFF: RAM
  • 0x800000-0x8FFFFF: ROM
  • 0x900000-0xEFFFFF: Nubus slot addresses
  • 0xF00000-0xFFFFFF: I/O

That particular model fits quite well with the currently implemented 24-bit memory manager, so we use that as a starting point for Color QuickDraw machine emulation. It also allows us to partially emulate slow manager APIs (as slot numbers $9 through $E match their address space as on real Macs), and allows possibility for emulating multiple screen using multiple “virtual” slot manager cards, one for each screen. The drawback of this, though, is that only one megabyte is assigned for each video device in 24-bit mode, which limits usable VRAM to that 1 megabyte. What this practically means, is that these are the approximately maximum supported “standard” resolutions for each color depth:

  • 1-bit (black & white): 3840 x 2160 (4K)
  • 2-bit (4-color): 2560 x 1440 (QHD)
  • 4-bit (16-color): 1920 x 1080 (FHD)
  • 8-bit (256-color): 1280 x 720 (HD)
  • 16-bit (32K colors): 832 x 624 (Mac 16″)
  • 32-bit (16.7M colors): 512 x 384 (Mac 12″)

Of course, when we later someday add 32-bit memory manager support, we will have 256 megabytes per video device, and can get rid of this limitation.

The slot driver

One key component between the “virtual” slot-based video device emulation, and the Color QuickDraw, is the device driver for the slot device. In our case, we added the .Display_Video_MACE_FB driver (following Apple’s naming convention for slot drivers), which is used by QuickDraw’s and Color Manager to control video modes, color table, etc.

On real Macs slot manager would be responsible for iterating parsing sRsrc:s and other slot-specific data structures, but we forego those hardware-specific details and address the native video device data (currently SDL) through our platform-abstraction interface.

The DRVR calls are still important to implement properly, as they were quite standard on real Macs, and there might be apps using them directly, even though well-behaving apps should always use GDevice, Color Manager and Color QuickDraw API calls.

Platform abstraction for color video

As we already had prepared for adding color support when starting the project two years ago, most of the support for it existed already in the platform abstraction layer. There were a couple tweaks needed, but most work was just adding the output renderers for each of the new color depths (originally there was only 1-bit blitter, as it was the only color depth supported on classic Macs). This also included adding the color lookup tables in the pipeline, so that we are ready for Palette Manager when we get to the point of implementing it.


As there may exist any number of screens, with any resolution and various color depths, Color QuickDraw added the concept of GDevices. Each GDevice represents one screen/video card attached to the system, with its own screen buffer, color & gamma tables, etc.

Color QuickDraw allows drawing to all of these devices at once using the standard toolbox API, doing all the color conversion and addressing for the user. This is what we need to implement next also in our emulator.

Color Manager

One key component of Color QuickDraw is Color Manager, which is responsible for managing the color tables for each GDevice. What this means, that it creates and manages the inverse color lookup tables (which are used to map RGB colors to indexed colors), and handles those lookups. It also keeps track of seed values for color tables, which are used to determine when color tables have changed, which is important especially if a previously expanded pattern is drawn after a new color table has been activated. For now, we implemented a very basic ITable generation for allowing RGBColors to work on indexed color modes.

Inverse color-lookup table

As meantioned above, one key feature of Color Manager is the generation and management of ITab data structures, which are used to map RGB Colors back into color table indices in indexed video modes (2-, 4- and 8-bit depths). The generator is run in MakeITable trap handler, which takes handle of color table, handle of output inverse table, and desired channel resolution as arguments.

The inverse table is actually a RGB cube, where the cube’s channel size is defined by the number of bits given as the resolution; so for example resolution of 4bits gives 2^4 = 16, and the entire RGB cube would take 16x16x16 bytes which is 4096 bytes, or 4K of memory. As in three-dimensional XYZ space, RGB cube can be thought of in the same way; Each R, G, B coordinate are used to locate index in the cube’s 3-dimensional table.

When Color QuickDraw wants to get for example, index of RGB color #E39EA0, Color Manager would convert first the RGB components into cube’s resolution range (in this case, result would be (14, 9, 10]), and use those values of index the ITab data to get the value.

When the cube is generated by MakeITable, it is initially empty, but is given the seed values from the source color table; each seed value is the color lookup table index, placed at the RGB coordinate which it specifies. After this, the seed values are progressively iterated, so that each value “spreads” into adjacent RGB cube slots in any of the six axis directions (+R/-R, +G/-G, +B/-B). This is repeated as long until there are no longer any unfilled slots left in the RGB cube. This is familiar method from basic pathfinding, and some maze generation algorithms, and ensures that each RGB cube slot contains the index of color lookup table which is the closest available approximation for that particular RGB color.

PixMaps (and PixPats)

As BitMaps only supported 1-bit graphics, Apple added PixMap in Color QuickDraw to allow representing graphics of any bit depth using a standard data structure. Additionally, the GDevices use PixMap to represent the VRAM buffers, and PixPat (multi-color patterns) structure also uses PixMap as storage for the pattern data. And they also are by default implemented as Handles, which means they can be moved in the heap during compaction to prevent memory fragmentation (but require locking in certain cases).

The first step: Using legacy GrafPorts with Color QuickDraw

As Color QuickDraw has a lot of layers to provide backwards-compatibility for older applications, the first step was to start from the most basic one, legacy GrafPort support. As the very first call done to QuickDraw is to gray out the screen at startup, we focused on getting the most basic case for FillRect working at first. With adding support for pattern expansion to any pixel depth, and adding new srcCopy blitters, we got this fist monochrome output result after a couple weeks of coding:

First 1-bit monochrome rectangles using Color QuickDraw in 640×480 mode

When emulating the old-style GrafPorts, of of their interesting features to simulate was support for the 8 old-style QuickDraw colors (which map mostly to the colors used in ImageWriter printers with CMYK ribbon). With proper color mapping, and a couple days of banging the head against desk, we ended up with this result:

Rectangles drawn in old-style 8-color GrafPort using Color QuickDraw

Second step: CGrafPort support

As mentioned earlier, the old-style GrafPorts were limited to only displaying those 8 colors, so to get the full range of RGB colors displayed, we had to add a proper CGrafPort support. This included implementing OpenCPort and InitCPort, and initialization of all related data structures. For example, all patterns in CGrafPorts are PixPat patterns, so we had to do a Pattern-to-PixPat conversion.

Most importantly, the fgColor/bkColor no longer represented the old-style color constants, but instead needed to be mapped to bit-depth specific index (on indexed device modes) or pixel value (on direct device modes). To control these colors, we implemented the RGBForeColor/RGBBackColor traps, which map the RGB values to the mode-specific values.

After a couple of days of more hard work, we now have the RGB colors working in CGrafPorts:

There is still A LOT of things to do before we can get much beyond simple rectangles on the screen, but the tasks should get easier as we go along. A lot of the routines (such as color mapping) can probably be shared as-is with most of other Color QuickDraw APIs. Some of the tasks next up are:

  • Adding region masking variant to the color blitter
  • Adding other pattern modes beyond patCopy
  • Adding source transfer modes (only patCopy done at the time of writing this)
  • Color versions of the special horizontal single-scanline blitters
  • A lot of other stuff

Full list of changes since last post

2020-01-31 18:02:57 +0200 • Basic support for "oldPat" PixPats in CGrafPorts
2020-01-31 16:35:14 +0200 • Implement InvertColor (default gdCompProc only!!!)
2020-01-31 13:47:55 +0200 • Some progress on CGrafPort colormapping & bugfixes
2020-01-30 02:10:42 +0200 • Add ColorQD Fore/BackColor & RGBFore/BackColor
2020-01-30 01:25:49 +0200 • Init default ColorQD PixPat patterns in InitCPort
2020-01-29 20:06:33 +0200 • Implement NewPixMap and NewPixPat
2020-01-29 01:42:41 +0200 • Initialize WMgrCPort (color port) in InitWindows
2020-01-29 01:41:59 +0200 • Implement OpenCPort and (mostly) InitCPort
2020-01-29 00:48:03 +0200 • Implement GetPixPat and GetCCursor colorQD traps
2020-01-28 22:12:56 +0200 • Implement DisposePixPat trap handler in color QD
2020-01-28 01:46:18 +0200 • Fix non-default colored patterns in 1-bit mode
2020-01-28 01:11:02 +0200 • ColorQD compatible GlobalToLocal/LocalToGlobal
2020-01-27 20:22:27 +0200 • Fix palette alignment issue in 8- and 15-bit modes
2020-01-27 20:20:38 +0200 • 15-bit (thousands of colors) SDL rendering support
2020-01-27 20:20:04 +0200 • 2-bit SDL output rendering support
2020-01-27 20:19:27 +0200 • Disable grayscale flag for now, test&fix it later
2020-01-27 20:18:37 +0200 • Fix last palette entry missing (zero-based count)
2020-01-27 13:33:46 +0200 • Add support for direct colors in color mapping
2020-01-27 13:26:34 +0200 • Set GDevice's gdType properly at initialization
2020-01-27 10:38:45 +0200 • GDev CLUT setup & rendering (first colors output!)
2020-01-27 09:44:47 +0200 • ColorQD ForeColor/BackColor in old-style GrafPorts
2020-01-27 09:43:56 +0200 • Fix initialization of QDColors low-mem global
2020-01-27 04:59:25 +0200 • Use Color2Index in color mapping for correct color
2020-01-27 04:56:41 +0200 • Set GDevice's gdResPref in the InitGDevice handler
2020-01-27 04:39:29 +0200 • Color2Index proto (no hidden color handling yet)
2020-01-27 04:36:27 +0200 • Fix the one-entry off "black-most black" index bug
2020-01-27 04:11:57 +0200 • Finish the first proto of MakeITable
2020-01-27 03:19:38 +0200 • Remove unneeded mitq resource from build
2020-01-27 03:18:51 +0200 • "Plant" seeds for the ITab generator from the clut
2020-01-26 00:24:21 +0200 • Start work on MakeITable
2020-01-26 00:23:50 +0200 • Tweak pattern blitters, preparing 8-bit support
2020-01-26 00:22:14 +0200 • Dummy Color2Index stub, prep use in colormapping
2020-01-25 17:05:21 +0200 • Hack 4- and 8-bit (16 & 256-color) output support
2020-01-25 17:01:45 +0200 • Fix old-type pattern to 8-bit conversion
2020-01-25 16:55:25 +0200 • Fix mask calculation for non-1-bit rectangle blits
2020-01-25 02:21:23 +0200 • First simple non-region FillRect case for ColorQD
2020-01-25 02:20:38 +0200 • Block attempting to post events before InitEvents
2020-01-25 02:19:04 +0200 • Fix the "dummy buffer" string RSAlloc overflow
2020-01-24 02:35:50 +0200 • Some progress on color blitter rectangle culling
2020-01-24 02:34:20 +0200 • Add QDErr low-mem global
2020-01-24 00:05:55 +0200 • Do CQD old 1-bit pattern to b&w GrafPort expansion
2020-01-23 00:18:35 +0200 • First CQD color mapping pass for old-type GrafPort
2020-01-22 17:53:29 +0200 • A bit of work on the color QD color mapping
2020-01-21 01:32:09 +0200 • Implement portBits to PixMap conversion to colorQD
2020-01-21 01:30:38 +0200 • Init lot of lowmem globals for default videodevice
2020-01-21 01:27:42 +0200 • Fix byteswap bug on device depth in CVGetVidParams
2020-01-20 15:02:02 +0200 • Refactor QD a bit in preparation of color support
2020-01-20 02:34:13 +0200 • Disable for now dirtyrect optimization in color QD
2020-01-20 02:22:37 +0200 • ColorQD versions of InitPort and OpenPort
2020-01-20 01:33:36 +0200 • Save LastMode/-Fore/-Back/-Depth in FMSwapFont
2020-01-20 01:32:29 +0200 • Fix two indexing bugs in ColorVideoInitOneSlot
2020-01-20 01:30:00 +0200 • Implement most of InitGDevice trap for color QD
2020-01-20 01:28:50 +0200 • Add empty stub for MakeITable trap
2020-01-19 23:29:53 +0200 • Add GetDeviceList trap
2020-01-19 20:37:49 +0200 • Add grayscale flag to video devices
2020-01-19 14:36:11 +0200 • Fill in GDevice's VPBlock from color video driver
2020-01-19 14:35:34 +0200 • Fill in DCE slot info in Open call for slot device
2020-01-19 05:03:02 +0200 • Add one more missing ROM clut resource
2020-01-19 05:02:32 +0200 • Add DisposePixMap, New/InitGDevice, GetNextDevice
2020-01-19 04:59:55 +0200 • Use cmake source_group TREE to clean up projects
2020-01-19 04:59:08 +0200 • Add MacVideo header
2020-01-18 23:54:18 +0200 • A couple more CQD resources (gama, mitq, cluts)
2020-01-18 05:51:16 +0200 • Add unit table debug dump tool to device manager
2020-01-18 05:50:37 +0200 • Add "virtual" slot DRVR installation support
2020-01-18 04:29:39 +0200 • Tweak video driver name & fix default slot amount
2020-01-18 04:26:22 +0200 • Implement DoVBLTask trap (untested)
2020-01-17 17:27:46 +0200 • Add SlotManager module + slot queue initialization
2020-01-17 01:52:09 +0200 • Implement color version of InitGraf
2020-01-17 01:28:37 +0200 • Add GetCTSeed/GetCTable/DisposeCTable to ColorMgr
2020-01-17 01:18:38 +0200 • Add TableSeed and HiliteRGB low-mem globals
2020-01-17 01:17:59 +0200 • Add default 'clut' tables to color ROM resources
2020-01-16 01:50:16 +0200 • Clean up linker errors for missing color QD stubs
2020-01-16 01:43:16 +0200 • Add setup of menubar 'mctb' color table (untested)
2020-01-16 01:35:33 +0200 • Empty stubs for GetCIcon, PlotCIcon & DisposeCIcon
2020-01-16 01:27:38 +0200 • GDevices module & GetMainDevice/GetMaxDevice stubs
2020-01-16 01:20:13 +0200 • Add empty stub for _ActivatePalette
2020-01-16 01:15:39 +0200 • Empty stubs for Delete/SetMCEntries & InitPalettes
2020-01-16 01:06:12 +0200 • Tweak ClassicSound to not fail colorQD compilation
2020-01-16 00:56:30 +0200 • Tweak some CMake configs for color-only apps
2020-01-16 00:55:31 +0200 • Refactor VBL code out of VIA + add slot# to video
2020-01-15 02:52:16 +0200 • Improve compilation of QDExtensions with color QD
2020-01-15 02:41:14 +0200 • Improve Menu Manager color QD compatibility
2020-01-15 02:40:40 +0200 • FMSwapFont color QD tweaks & LastSPExtra type fix
2020-01-15 02:36:37 +0200 • Fix ClassicSound compile error w/o Sound driver
2020-01-15 00:49:29 +0200 • Separate Mono & Color fake roms + add 32-mode flag
2020-01-15 00:47:24 +0200 • Add the DRVR 120 (.Display_Video_MACE) to fake rom
2020-01-15 00:45:59 +0200 • Add color video initialization call to boot code
2020-01-15 00:44:02 +0200 • Add stub for the color video driver
2020-01-15 00:42:54 +0200 • Add symbol name to binary-to-C converter