gba.c

#include "gba.h" // Mode 0 Scaffold

// The start of the video memory
unsigned volatile short *videoBuffer = (unsigned short *)0x6000000;


// ---- Miscellaneous Functions ----

int collision(int colA, int rowA, int widthA, int heightA, int colB, int rowB, int widthB, int heightB) {
    return rowA <= rowB + heightB - 1 && rowA + heightA - 1 >= rowB && colA <= colB + widthB - 1 && colA + widthA - 1 >= colB;
}

void waitForVBlank() {
    while (SCANLINECOUNTER >= 160);
    while (SCANLINECOUNTER < 160);
}


// ---- Mode 3 ----

void setPixel3(int col, int row, unsigned short color) {
    videoBuffer[OFFSET(col, row, SCREENWIDTH)] = color;
}

void drawRect3(int col, int row, int width, int height, volatile unsigned short color) {
    for (int r = 0; r < height; r++) {
        DMANow(3, &color, &videoBuffer[OFFSET(col, row + r, SCREENWIDTH)], DMA_SOURCE_FIXED | width);
    }
}

void fillScreen3(volatile unsigned short color) {
    unsigned short c = color;
    DMANow(3, &c, videoBuffer, DMA_SOURCE_FIXED | (SCREENWIDTH * SCREENHEIGHT));
}

void drawImage3(int col, int row, int width, int height, const unsigned short *image) {
    for (int r = 0; r < height; r++) {
        DMANow(3, &image[OFFSET(0, r, width)], &videoBuffer[OFFSET(col, row + r, SCREENWIDTH)], width);
    }
}

void drawFullscreenImage3(const unsigned short *image) {
    DMANow(3, image, videoBuffer, SCREENWIDTH * SCREENHEIGHT);
}


// ---- Mode 4 ----

void drawImage4(int col, int row, int width, int height, const unsigned short *image) {
    for (int i = 0; i < height; i++) {
        DMANow(3, &image[OFFSET(0, i, width / 2)], &videoBuffer[OFFSET(col, row + i, SCREENWIDTH) / 2], width / 2);
    }
}

void setPixel4(int col, int row, unsigned char colorIndex) {
    volatile unsigned short pixelData = videoBuffer[OFFSET(col, row, SCREENWIDTH) / 2];
    if (col & 1) {
        pixelData &= 0x00FF;
        pixelData |= colorIndex << 8;
    } else {
        pixelData &= 0xFF00;
        pixelData |= colorIndex;
    }
    videoBuffer[OFFSET(col, row, SCREENWIDTH) / 2] = pixelData;
}

void drawRect4(int col, int row, int width, int height, volatile unsigned char colorIndex) {
    volatile unsigned short pixelData = colorIndex | (colorIndex << 8);
    for (int r = 0; r < height; r++) {
        // Ensure we don't DMA 0 copies
        if (width == 1) {
            setPixel4(col, row + r, colorIndex);
        } else if (width == 2) {
            setPixel4(col, row + r, colorIndex);
            setPixel4(col + 1, row + r, colorIndex);
        } else if ((col & 1) && (width & 1)) /* Odd width odd col */ {
            setPixel4(col, row + r, colorIndex);
            DMANow(3, &pixelData, &videoBuffer[OFFSET(col + 1, row + r, SCREENWIDTH) / 2], DMA_SOURCE_FIXED | (width - 1) / 2);
        } else if (width & 1) /* Even col odd width */ {
            DMANow(3, &pixelData, &videoBuffer[OFFSET(col, row + r, SCREENWIDTH) / 2], DMA_SOURCE_FIXED | (width - 1) / 2);
            setPixel4(col + width - 1, row + r, colorIndex);
        } else if (col & 1) /* Odd col even width */ {
            setPixel4(col, row + r, colorIndex);
            DMANow(3, &pixelData, &videoBuffer[OFFSET(col + 1, row + r, SCREENWIDTH) / 2], DMA_SOURCE_FIXED | (width - 2) / 2);
            setPixel4(col + width - 1, row + r, colorIndex);
        } else /* Even col even width */ {
            DMANow(3, &pixelData, &videoBuffer[OFFSET(col, row + r, SCREENWIDTH) / 2], DMA_SOURCE_FIXED | width / 2);
        }
    }
}

void fillScreen4(volatile unsigned char colorIndex) {
    volatile unsigned short pixelData = colorIndex | (colorIndex << 8);
    DMANow(3, &pixelData, videoBuffer, DMA_SOURCE_FIXED | (SCREENWIDTH * SCREENHEIGHT) / 2);
}

void drawFullscreenImage4(const unsigned short *image) {
    DMANow(3, image, videoBuffer, SCREENWIDTH * SCREENHEIGHT / 2);
}

void flipPage() {
    if (REG_DISPCTL & DISP_BACKBUFFER) {
        videoBuffer = BACKBUFFER;
    } else {
        videoBuffer = FRONTBUFFER;
    }
    REG_DISPCTL ^= DISP_BACKBUFFER;
}


// ---- DMA ----

// The start of DMA registers
DMA *dma = (DMA *)0x40000B0;

void DMANow(int channel, volatile const void *src, volatile void *dst, unsigned int cnt) {
    dma[channel].cnt = 0;

    dma[channel].src = src;
    dma[channel].dst = dst;

    dma[channel].cnt = cnt | DMA_ON;
}


// ---- Sprites ----

// Hides all sprites in the shadowOAM; Must DMA the shadowOAM into the OAM after calling this function
void hideSprites() {
    for (int i = 0; i < 128; i++) {
        shadowOAM[i].attr0 = ATTR0_HIDE;
    }
}