Pixel Mixer
The Propeller 2 supports a set of four "Pixel Mixer" instructions that are designed to accelerate operations on graphics data, particularily 32 bit RGBA and 8 bit greyscale formats. For 16 bit RGB support, see RGBEXP and RGBSQZ.
All pixel mixer operations perform the following math:
\[\newcommand{\DMIX}{\mathit{DMIX}} \newcommand{\SMIX}{\mathit{SMIX}} D'[31:24] \approx \min\left({{D[31:24] *\DMIX+S[31:24] *\SMIX+255}\over 256},255\right) \\ D'[23:16] \approx \min\left({{D[23:16] *\DMIX+S[23:16] *\SMIX+255}\over 256},255\right) \\ D'[15:~~8] \approx \min\left({{D[15:~~8] *\DMIX+S[15:~~8] *\SMIX+255}\over 256},255\right) \\ D'[~~7:~~0] \approx \min\left({{D[~~7:~~0] *\DMIX+S[~~7:~~0] *\SMIX+255}\over 256},255\right)\]wherein DMIX and SMIX depend on the instruction:
| Instr. | DMIX | SMIX |
|---|---|---|
| ADDPIX | 255 | 255 |
| MULPIX | S[byte] | 0 |
| BLNPIX | 255 - PIV | PIV |
| MIXPIX | PIX[5:3] = %000 -> 0 PIX[5:3] = %001 -> 255 PIX[5:3] = %010 -> PIV PIX[5:3] = %011 -> 255 - PIV PIX[5:3] = %100 -> S[byte] PIX[5:3] = %101 -> 255 - S[byte] PIX[5:3] = %110 -> D[byte] PIX[5:3] = %111 -> 255 - D[byte] | PIX[2:0] = %000 -> 0 PIX[2:0] = %001 -> 255 PIX[2:0] = %010 -> PIV PIX[2:0] = %011 -> 255 - PIV PIX[2:0] = %100 -> S[byte] PIX[2:0] = %101 -> 255 - S[byte] PIX[2:0] = %110 -> D[byte] PIX[2:0] = %111 -> 255 - D[byte] |
The equivalent SETPIX value for ADDPIX is %001_001.
The equivalent SETPIX value for MULPIX is %100_000.
The equivalent SETPIX value for BLNPIX is %011_010.
Instructions
ADDPIX D,{#}S - Add colors
| Encoding | Register Written | C Flag | Z Flag | Cycles (cogexec) | Cycles (hubexec) | IRQ Shield | EEEE 1010010 00I DDDDDDDDD SSSSSSSSS | D | --- | --- | 7 | 7 | No |
|---|
ADDPIX performs a per-byte saturated addition of Source into Destination. I.e. if the addition of a byte overflows, the result is capped to 255.
\[D'[31:24] = \min\left({D[31:24]+S[31:24]},255\right) \\ D'[23:16] = \min\left({D[23:16]+S[23:16]},255\right) \\ D'[15:~~8] = \min\left({D[15:~~8]+S[15:~~8]},255\right) \\ D'[~~7:~~0] = \min\left({D[~~7:~~0]+S[~~7:~~0]},255\right)\]MULPIX D,{#}S - Multiply colors
| Encoding | Register Written | C Flag | Z Flag | Cycles (cogexec) | Cycles (hubexec) | IRQ Shield | EEEE 1010010 01I DDDDDDDDD SSSSSSSSS | D | --- | --- | 7 | 7 | No |
|---|
BLNPIX D,{#}S - Blend between colors
| Encoding | Register Written | C Flag | Z Flag | Cycles (cogexec) | Cycles (hubexec) | IRQ Shield | EEEE 1010010 10I DDDDDDDDD SSSSSSSSS | D | --- | --- | 7 | 7 | No |
|---|
MIXPIX D,{#}S - Generic color mixing operation
| Encoding | Register Written | C Flag | Z Flag | Cycles (cogexec) | Cycles (hubexec) | IRQ Shield | EEEE 1010010 11I DDDDDDDDD SSSSSSSSS | D | --- | --- | 7 | 7 | No |
|---|
MIXPIX performs an arbitrary pixel mix operation between Source and Destination, as configured by SETPIX. Also see above.
TODO more