nt-lite/code/hal/hal_screen.c

// hal_screen.c - GOP framebuffer screen driver with embedded 8x16 font
//
// The 8x16 bitmap font is a standard VGA/PC font.  We embed just the
// printable ASCII range (0x20–0x7E).  Each glyph is 16 bytes; bit 7 of
// each byte is the leftmost pixel.
#include "hal_api.h"
#include <stdint.h>
#include <string.h>
#include <intrin.h>

static uint32_t* gFb     = (uint32_t *)0;
static int       gWidth  = 0;
static int       gHeight = 0;
static int       gStride = 0;  // pixels per row
static int       gCursorX = 0, gCursorY = 0;

#define FONT_W 8
#define FONT_H 16

// ---------------------------------------------------------------------------
// 8x16 VGA font - printable ASCII only (glyph 0 = space = 0x20)
// ---------------------------------------------------------------------------
#include "font8x16.h"   // see font8x16.h below

// ---------------------------------------------------------------------------
// Internals
// ---------------------------------------------------------------------------
static inline void PutPixelRaw(int x, int y, uint32_t color) {
    if ((unsigned)x < (unsigned)gWidth && (unsigned)y < (unsigned)gHeight)
        gFb[y * gStride + x] = color;
}

// ---------------------------------------------------------------------------
// HAL_SCREEN implementations
// ---------------------------------------------------------------------------
static void ScreenClear(uint32_t color) {
    for (int y = 0; y < gHeight; y++)
        for (int x = 0; x < gWidth; x++)
            gFb[y * gStride + x] = color;
    gCursorX = 0; gCursorY = 0;
}

static void ScreenPutPixel(int x, int y, uint32_t color) {
    PutPixelRaw(x, y, color);
}

static void ScreenBlit(int x, int y, int w, int h, const uint32_t* pixels) {
    // Calculate clipping bounds
    int startX = (x < 0) ? 0 : x;
    int startY = (y < 0) ? 0 : y;
    int endX = (x + w > gWidth) ? gWidth : (x + w);
    int endY = (y + h > gHeight) ? gHeight : (y + h);

    int drawW = endX - startX;
    int drawH = endY - startY;

    // If the image is entirely off-screen, do nothing
    if (drawW <= 0 || drawH <= 0) {
        return;
    }

    // Adjust the source pointer if the image was clipped on the top or left
    int srcOffsetX = startX - x;
    int srcOffsetY = startY - y;

    // Calculate bytes to copy per row
    size_t bytesPerRow = (size_t)drawW * sizeof(uint32_t);

    // If the width we are drawing exactly matches the physical screen stride,
    // AND it matches the original source image width, memory is perfectly contiguous.
    if (drawW == gStride && drawW == w) {
        uint32_t* dst = gFb + (startY * gStride) + startX;
        const uint32_t* src = pixels + (srcOffsetY * w) + srcOffsetX;
        
        memcpy(dst, src, bytesPerRow * drawH);
        return;
    }

    // Copy row-by-row
    for (int row = 0; row < drawH; row++) {
        // Destination in the actual framebuffer (accounting for stride)
        uint32_t* dst = gFb + ((startY + row) * gStride) + startX;
        
        // Source from the provided pixel buffer
        const uint32_t* src = pixels + ((srcOffsetY + row) * w) + srcOffsetX;
        
        memcpy(dst, src, bytesPerRow);
    }
}

static void ScreenGetSize(int* w, int* h) { *w = gWidth; *h = gHeight; }

static void ScreenScroll(int lines) {
    if (lines <= 0 || lines >= gHeight) { ScreenClear(0); return; }
    int rowBytes = gStride * sizeof(uint32_t);
    memmove(gFb, gFb + lines * gStride,
            (size_t)(gHeight - lines) * rowBytes);
    // Clear the revealed rows at the bottom.
    memset(gFb + (gHeight - lines) * gStride, 0,
           (size_t)lines * rowBytes);
}

static void ScreenPutChar(char c, int x, int y, uint32_t fg, uint32_t bg) {
    if ((unsigned char)c < 0x20 || (unsigned char)c > 0x7E) c = '?';
    const uint8_t* glyph = Font8x16 + ((unsigned char)c - 0x20) * 16;
    for (int row = 0; row < 16; row++) {
        uint8_t bits = glyph[row];
        for (int col = 0; col < 8; col++) {
            uint32_t color = (bits & (1 << col)) ? fg : bg; // i don't know why, i don't want to know why
            // i shouldn't have to wonder why but the font is backwards unless we do this terriblness
            PutPixelRaw(x + col, y + row, color);
        }
    }
}

static void ScreenPrintChar(char c, uint32_t fg, uint32_t bg) {
    int cols = gWidth  / FONT_W;
    int rows = gHeight / FONT_H;

    // Mirror to serial
    while ((__inbyte(0x3FD) & 0x20) == 0);
    if (c == '\n') __outbyte(0x3F8, '\r');
    __outbyte(0x3F8, c);

    if (c == '\n') {
        gCursorX = 0;
        gCursorY++;
    } else if (c == '\r') {
        gCursorX = 0;
    } else if (c == '\b') {
        if (gCursorX > 0) {
            gCursorX--;
        } else if (gCursorY > 0) {
            gCursorY--;
            gCursorX = cols - 1;
        }
    } else {
        ScreenPutChar(c, gCursorX * FONT_W, gCursorY * FONT_H, fg, bg);
        if (++gCursorX >= cols) { gCursorX = 0; gCursorY++; }
    }
    if (gCursorY >= rows) {
        ScreenScroll(FONT_H);
        gCursorY = rows - 1;
    }
}

// ---------------------------------------------------------------------------
// Populate the HAL_SCREEN vtable
// ---------------------------------------------------------------------------
void HalScreenInitialize(uintptr_t fb, int w, int h, int stride,
                         HAL_SCREEN* out) {
    gFb     = (uint32_t *)fb;
    gWidth  = w;
    gHeight = h;
    gStride = stride;
    out->Clear    = ScreenClear;
    out->PutPixel = ScreenPutPixel;
    out->Blit     = ScreenBlit;
    out->GetSize  = ScreenGetSize;
    out->Scroll   = ScreenScroll;
    out->PutChar  = ScreenPutChar;
    out->PrintChar = ScreenPrintChar;
    ScreenClear(0x000000);
}