sprite.S

/*
 * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

// Functions for doing simple 2D graphics operations on a RGB scanline buffer.

#include "hardware/regs/addressmap.h"
#include "hardware/regs/sio.h"

#define POP2_OFFS (SIO_INTERP0_POP_FULL_OFFSET - SIO_INTERP0_ACCUM0_OFFSET)
#define CTRL0_OFFS (SIO_INTERP0_CTRL_LANE0_OFFSET - SIO_INTERP0_ACCUM0_OFFSET)
#define INTERP1 (SIO_INTERP1_ACCUM0_OFFSET - SIO_INTERP0_ACCUM0_OFFSET)

.syntax unified
.cpu cortex-m0plus
.thumb

// Put every function in its own ELF section, to permit linker GC
.macro decl_func name
.section .time_critical.\name, "ax"
.global \name
.type \name,%function
.thumb_func
\name:
.endm

// ----------------------------------------------------------------------------
// Colour fill

// r0: dst
// r1: value
// r2: count

decl_func sprite_fill8
    // Slide for short fills
    cmp r2, #18
    bhi 2f
    adr r3, 1f
    lsls r2, #1
    subs r3, r2
    adds r3, #1 // thumb bit
    bx r3
.align 2
    strb r1, [r0, #17]
    strb r1, [r0, #16]
    strb r1, [r0, #15]
    strb r1, [r0, #14]
    strb r1, [r0, #13]
    strb r1, [r0, #12]
    strb r1, [r0, #11]
    strb r1, [r0, #10]
    strb r1, [r0, #9]
    strb r1, [r0, #8]
    strb r1, [r0, #7]
    strb r1, [r0, #6]
    strb r1, [r0, #5]
    strb r1, [r0, #4]
    strb r1, [r0, #3]
    strb r1, [r0, #2]
    strb r1, [r0, #1]
    strb r1, [r0, #0]
1:
    bx lr
2:
    lsls r3, r1, #8
    orrs r1, r3
    lsls r3, r1, #16
    orrs r1, r3
    // Get r0 word-aligned:
    lsrs r3, r0, #1
    bcc 1f
    strb r1, [r0]
    adds r0, #1
    subs r2, #1
1:
    lsrs r3, r0, #2
    bcc 1f
    strh r1, [r0]
    adds r0, #2
    subs r2, #2
1:
    // Set up for main loop. Limit pointer at end - (loop body size - 1)
    push {r4}
    adds r2, r0
    subs r2, #15
    mov ip, r2
    mov r2, r1
    mov r3, r1
    mov r4, r1

    // Fall straight into loop, because cases less than (loop body + max misalignment) are handled by slide
1:
    stmia r0!, {r1, r2, r3, r4}
    cmp r0, ip
    blo 1b

    // Main loop done, now tidy up the odds and ends
    mov r4, ip
    subs r4, r0
    adds r4, #15
    // No more than 15 bytes remaining -- first test bit 3
    lsls r4, #29
    bcc 1f
    stmia r0!, {r1, r2}
1:
    lsls r4, #1
    bcc 1f
    stmia r0!, {r1}
1:
    lsls r4, #1
    bcc 1f
    strh r1, [r0]
    adds r0, #2
1:
    lsls r4, #1
    bcc 1f
    strb r1, [r0]
1:
    pop {r4}
    bx lr


decl_func sprite_fill16
    // Slide for short fills
    cmp r2, #15
    bhi 2f
    adr r3, 1f
    lsls r2, #1
    subs r3, r2
    adds r3, #1
    bx r3
.align 2
    strh r1, [r0, #30]
    strh r1, [r0, #28]
    strh r1, [r0, #26]
    strh r1, [r0, #24]
    strh r1, [r0, #22]
    strh r1, [r0, #20]
    strh r1, [r0, #18]
    strh r1, [r0, #16]
    strh r1, [r0, #14]
    strh r1, [r0, #12]
    strh r1, [r0, #10]
    strh r1, [r0, #8]
    strh r1, [r0, #6]
    strh r1, [r0, #4]
    strh r1, [r0, #2]
    strh r1, [r0, #0]
1:
    bx lr
2:
    push {r4, r5, r6, r7, lr}
    // Get word-aligned before main fill loop
    lsrs r3, r2, #2
    bcc 1f
    strh r1, [r0]
    adds r0, #2
    subs r2, #1
1:
    // Set limit pointer at end - (loop body size - 1)
    lsls r2, #1
    adds r2, r0
    subs r2, #26
    mov ip, r2

    lsls r2, r1, #16
    orrs r1, r2
    mov r2, r1
    mov r3, r1
    mov r4, r1
    mov r5, r1
    mov r6, r1
    mov r7, r1
    // We can fall through because cases < 1 loop are handled by slide
1:
    stmia r0!, {r1, r2, r3, r4, r5, r6, r7} // wheeeeeeeeeee
    cmp r0, ip
    blo 1b

    // Most of the work done, we have a few more to tidy up
    movs r2, #26
    add r2, ip
    subs r2, r0

    lsls r2, #28
    bcc 1f
    stmia r0!, {r4, r5, r6, r7}
1:
    lsls r2, #1
    bcc 1f
    stmia r0!, {r4, r5}
1:
    lsls r2, #1
    bcc 1f
    stmia r0!, {r4}
1:
    lsls r2, #1
    bcc 1f
    strh r4, [r0]
1:
    pop {r4, r5, r6, r7, pc}

// ----------------------------------------------------------------------------
// Non-AT sprite

// r0: dst
// r1: src
// r2: pixel count
//

// Unrolled loop body with an initial computed branch. Note we can go much
// faster if r0 and r1 are co-aligned, but it's not all that helpful to have a
// 1 in 4 chance of being really fast when minimising worst-case scanline time

decl_func sprite_blit8
    mov ip, r0
    lsrs r3, r2, #3
    lsls r3, #3
    eors r2, r3   // r2 = pixels % 8, r3 = pixels = pixels % 8

    add r0, r3
    add r1, r3

    adr r3, 2f
    lsls r2, #2
    subs r3, r2
    adds r3, #1 // thumb bit >:(
    bx r3

.align 2
1:
    subs r0, #8
    subs r1, #8
    ldrb r3, [r1, #7]
    strb r3, [r0, #7]
    ldrb r3, [r1, #6]
    strb r3, [r0, #6]
    ldrb r3, [r1, #5]
    strb r3, [r0, #5]
    ldrb r3, [r1, #4]
    strb r3, [r0, #4]
    ldrb r3, [r1, #3]
    strb r3, [r0, #3]
    ldrb r3, [r1, #2]
    strb r3, [r0, #2]
    ldrb r3, [r1, #1]
    strb r3, [r0, #1]
    ldrb r3, [r1, #0]
    strb r3, [r0, #0]
2:
    cmp r0, ip
    bhi 1b
    bx lr

// Assume RAGB2132 (so alpha is bit 5)

#define ALPHA_SHIFT_8BPP 6

.macro sprite_blit8_alpha_body n
    ldrb r3, [r1, #\n]
    lsrs r2, r3, #ALPHA_SHIFT_8BPP
    bcc 2f
    strb r3, [r0, #\n]
2:
.endm

decl_func sprite_blit8_alpha
    mov ip, r0
    lsrs r3, r2, #3
    lsls r3, #3
    eors r2, r3

    add r0, r3
    add r1, r3

    adr r3, 3f
    lsls r2, #3
    subs r3, r2
    adds r3, #1
    bx r3

.align 2
1:
    subs r0, #8
    subs r1, #8
    sprite_blit8_alpha_body 7
    sprite_blit8_alpha_body 6
    sprite_blit8_alpha_body 5
    sprite_blit8_alpha_body 4
    sprite_blit8_alpha_body 3
    sprite_blit8_alpha_body 2
    sprite_blit8_alpha_body 1
    sprite_blit8_alpha_body 0
3:
    cmp r0, ip
    bhi 1b
    bx lr


decl_func sprite_blit16
    mov ip, r0
    lsrs r3, r2, #3
    lsls r3, #3
    eors r2, r3   // r2 = pixels % 8, r3 = pixels = pixels % 8

    lsls r3, #1
    add r0, r3
    add r1, r3

    adr r3, 2f
    lsls r2, #2
    subs r3, r2
    adds r3, #1 // thumb bit >:(
    bx r3

.align 2
1:
    subs r0, #16
    subs r1, #16
    ldrh r3, [r1, #14]
    strh r3, [r0, #14]
    ldrh r3, [r1, #12]
    strh r3, [r0, #12]
    ldrh r3, [r1, #10]
    strh r3, [r0, #10]
    ldrh r3, [r1, #8]
    strh r3, [r0, #8]
    ldrh r3, [r1, #6]
    strh r3, [r0, #6]
    ldrh r3, [r1, #4]
    strh r3, [r0, #4]
    ldrh r3, [r1, #2]
    strh r3, [r0, #2]
    ldrh r3, [r1, #0]
    strh r3, [r0, #0]
2:
    cmp r0, ip
    bhi 1b
    bx lr

// Assume RGAB5515 (so alpha is bit 5)
// Note the alpha bit being in the same position as RAGB2132 is a coincidence.
// We are just stealing an LSB such that we can treat our alpha pixels in the
// same way as non-alpha pixels when encoding (and the co-opted channel LSB
// always ends up being set on alpha pixels, which is pretty harmless)

#define ALPHA_SHIFT_16BPP 6

.macro sprite_blit16_alpha_body n
    ldrh r3, [r1, #2*\n]
    lsrs r2, r3, #ALPHA_SHIFT_16BPP
    bcc 2f
    strh r3, [r0, #2*\n]
2:
.endm

decl_func sprite_blit16_alpha
    mov ip, r0
    lsrs r3, r2, #3
    lsls r3, #3
    eors r2, r3

    lsls r3, #1
    add r0, r3
    add r1, r3

    adr r3, 3f
    lsls r2, #3
    subs r3, r2
    adds r3, #1
    bx r3

.align 2
1:
    subs r0, #16
    subs r1, #16
    sprite_blit16_alpha_body 7
    sprite_blit16_alpha_body 6
    sprite_blit16_alpha_body 5
    sprite_blit16_alpha_body 4
    sprite_blit16_alpha_body 3
    sprite_blit16_alpha_body 2
    sprite_blit16_alpha_body 1
    sprite_blit16_alpha_body 0
3:
    cmp r0, ip
    bhi 1b
    bx lr


// ----------------------------------------------------------------------------
// Affine-transformed sprite (note these are just the inner loops -- INTERP0
// must be configured by the caller, which is presumably not written in asm)

// r0: raster start pointer
// r1: raster span size (pixels)

.macro sprite_ablit8_loop_body n
    ldr r1, [r3, #CTRL0_OFFS]
    ldr r2, [r3, #POP2_OFFS]
    lsrs r1, #SIO_INTERP0_CTRL_LANE0_OVERF_LSB + 1
    bcs 2f
    ldrb r2, [r2]
    strb r2, [r0, #\n]
2:
.endm

decl_func sprite_ablit8_loop
    mov ip, r0

    lsrs r2, r1, #3
    lsls r2, #3
    eors r1, r2
    add r0, r2

    adr r2, 3f
    movs r3, #12 // Each (non-unrolled) loop body is 12 bytes
    muls r1, r3
    subs r2, r1
    adds r2, #1

    ldr r3, =(SIO_BASE + SIO_INTERP0_ACCUM0_OFFSET)
    bx r2

.align 2
    nop
1:
    subs r0, #8
    sprite_ablit8_loop_body 7
    sprite_ablit8_loop_body 6
    sprite_ablit8_loop_body 5
    sprite_ablit8_loop_body 4
    sprite_ablit8_loop_body 3
    sprite_ablit8_loop_body 2
    sprite_ablit8_loop_body 1
    sprite_ablit8_loop_body 0
3:
    cmp r0, ip
    bne 1b
    bx lr



// As above but bit 5 is assumed to be an alpha bit (RAGB2132)

.macro sprite_ablit8_alpha_loop_body n
    ldr r1, [r3, #CTRL0_OFFS]
    ldr r2, [r3, #POP2_OFFS]
    lsrs r1, #SIO_INTERP0_CTRL_LANE0_OVERF_LSB + 1
    bcs 2f
    ldrb r2, [r2]
    lsrs r1, r2, #ALPHA_SHIFT_8BPP
    bcc 2f
    strb r2, [r0, #\n]
2:
.endm

decl_func sprite_ablit8_alpha_loop
    mov ip, r0
    ldr r3, =(SIO_BASE + SIO_INTERP0_ACCUM0_OFFSET)

    lsrs r2, r1, #3
    lsls r2, #3
    eors r1, r2
    add r0, r2

    adr r2, 3f
    lsls r1, #4 // Each (non-unrolled) loop body is 16 bytes
    subs r2, r1
    adds r2, #1
    bx r2

.align 2
    nop
1:
    subs r0, #8
    sprite_ablit8_alpha_loop_body 7
    sprite_ablit8_alpha_loop_body 6
    sprite_ablit8_alpha_loop_body 5
    sprite_ablit8_alpha_loop_body 4
    sprite_ablit8_alpha_loop_body 3
    sprite_ablit8_alpha_loop_body 2
    sprite_ablit8_alpha_loop_body 1
    sprite_ablit8_alpha_loop_body 0
3:
    cmp r0, ip
    bhi 1b
    bx lr



.macro sprite_ablit16_loop_body n
    ldr r1, [r3, #CTRL0_OFFS]
    ldr r2, [r3, #POP2_OFFS]
    lsrs r1, #SIO_INTERP0_CTRL_LANE0_OVERF_LSB + 1
    bcs 2f
    ldrh r2, [r2]
    strh r2, [r0, #2*\n]
2:
.endm

decl_func sprite_ablit16_loop
    mov ip, r0

    lsrs r2, r1, #3
    lsls r2, #3
    eors r1, r2
    lsls r2, #1 // Each pixel is 2 bytes
    add r0, r2

    adr r2, 3f
    movs r3, #12 // Each (non-unrolled) loop body is 12 bytes
    muls r1, r3
    subs r2, r1
    adds r2, #1

    ldr r3, =(SIO_BASE + SIO_INTERP0_ACCUM0_OFFSET)
    bx r2

.align 2
    nop
1:
    subs r0, #16
    sprite_ablit16_loop_body 7
    sprite_ablit16_loop_body 6
    sprite_ablit16_loop_body 5
    sprite_ablit16_loop_body 4
    sprite_ablit16_loop_body 3
    sprite_ablit16_loop_body 2
    sprite_ablit16_loop_body 1
    sprite_ablit16_loop_body 0
3:
    cmp r0, ip
    bne 1b
    bx lr



.macro sprite_ablit16_alpha_loop_body n
    ldr r1, [r3, #CTRL0_OFFS]
    ldr r2, [r3, #POP2_OFFS]
    lsrs r1, #SIO_INTERP0_CTRL_LANE0_OVERF_LSB + 1
    bcs 2f
    ldrh r2, [r2]
    lsrs r1, r2, #ALPHA_SHIFT_16BPP
    bcc 2f
    strh r2, [r0, #2*\n]
2:
.endm

decl_func sprite_ablit16_alpha_loop
    mov ip, r0
    ldr r3, =(SIO_BASE + SIO_INTERP0_ACCUM0_OFFSET)

    lsrs r2, r1, #3
    lsls r2, #3
    eors r1, r2
    lsls r2, #1 // Each pixel is 2 bytes
    add r0, r2

    adr r2, 3f
    lsls r1, #4 // Each (non-unrolled) loop body is 16 bytes
    subs r2, r1
    adds r2, #1
    bx r2

.align 2
    nop
1:
    subs r0, #16
    sprite_ablit16_alpha_loop_body 7
    sprite_ablit16_alpha_loop_body 6
    sprite_ablit16_alpha_loop_body 5
    sprite_ablit16_alpha_loop_body 4
    sprite_ablit16_alpha_loop_body 3
    sprite_ablit16_alpha_loop_body 2
    sprite_ablit16_alpha_loop_body 1
    sprite_ablit16_alpha_loop_body 0
3:
    cmp r0, ip
    bhi 1b
    bx lr