ATItoTGA normal map generation

[Josh]

I have always loved the normal maps ATItoDOT3 produces. Here is an implementation using their algorithm grabbed from here:
https://github.com/mojocorp/ATINormalMapper/blob/master/TGAtoDOT3/TGAtoDOT3.cpp

 

#include "UltraEngine.h"

using namespace UltraEngine;

typedef struct _pixel
{
    uint8 red;
    uint8 blue;
    uint8 green;
    uint8 alpha;
} pixel;

inline void
TGAReadPixel(uint8* image, int width, int off, pixel* pix, int x, int y)
{
#ifdef _DEBUG
    if ((image == NULL) || (pix == NULL)) {
        //NmPrint("ERROR: NULL pointer passed to Readpixel!\n");
        exit(-1);
    }
#endif
    int idx = y * width * off + x * off;
    if (off > 0) {
        pix->red = image[idx];
    }
    if (off > 1) {
        pix->blue = image[idx + 1];
    }
    if (off > 2) {
        pix->green = image[idx + 2];
    }
}

int gWidth, gHeight;

void
WritePixel(uint8* image, int bpp, const pixel* pix, int x, int y)
{
    const int idx = (x + y * gWidth) * (bpp / 8);
    if (bpp >= 8) {
        image[idx + 0] = pix->blue;
    }
    if (bpp >= 16) {
        image[idx + 1] = pix->green;
    }
    if (bpp >= 24) {
        image[idx + 2] = pix->red;
    }
    if (bpp >= 32) {
        image[idx + 3] = pix->alpha;
    }
}

uint8
PackFloatInByte(float in)
{
    return (uint8)((in + 1.0f) / 2.0f * 255.0f);
}

void
SobelFilter(uint8* dstImage, uint8* srcImage, int width, int height, int bpp)
{
    gWidth = width;
    gHeight = height;
    pixel pix;
    for (int y = 0; y < height; y++) {
        for (int x = 0; x < width; x++) {
            // Do Y Sobel filter
            TGAReadPixel(srcImage, width, bpp / 8, &pix, (x - 1 + width) % width, (y + 1) % height);
            float dY = ((float)pix.red) / 255.0f * -1.0f;

            TGAReadPixel(srcImage, width, bpp / 8, &pix, x % width, (y + 1) % height);
            dY += ((float)pix.red) / 255.0f * -2.0f;

            TGAReadPixel(srcImage, width, bpp / 8, &pix, (x + 1) % width, (y + 1) % height);
            dY += ((float)pix.red) / 255.0f * -1.0f;

            TGAReadPixel(
                srcImage, width, bpp / 8, &pix, (x - 1 + width) % width, (y - 1 + height) % height);
            dY += ((float)pix.red) / 255.0f * 1.0f;

            TGAReadPixel(srcImage, width, bpp / 8, &pix, x % width, (y - 1 + height) % height);
            dY += ((float)pix.red) / 255.0f * 2.0f;

            TGAReadPixel(
                srcImage, width, bpp / 8, &pix, (x + 1) % width, (y - 1 + height) % height);
            dY += ((float)pix.red) / 255.0f * 1.0f;

            // Do X Sobel filter
            TGAReadPixel(
                srcImage, width, bpp / 8, &pix, (x - 1 + width) % width, (y - 1 + height) % height);
            float dX = ((float)pix.red) / 255.0f * -1.0f;

            TGAReadPixel(srcImage, width, bpp / 8, &pix, (x - 1 + width) % width, y % height);
            dX += ((float)pix.red) / 255.0f * -2.0f;

            TGAReadPixel(srcImage, width, bpp / 8, &pix, (x - 1 + width) % width, (y + 1) % height);
            dX += ((float)pix.red) / 255.0f * -1.0f;

            TGAReadPixel(
                srcImage, width, bpp / 8, &pix, (x + 1) % width, (y - 1 + height) % height);
            dX += ((float)pix.red) / 255.0f * 1.0f;

            TGAReadPixel(srcImage, width, bpp / 8, &pix, (x + 1) % width, y % height);
            dX += ((float)pix.red) / 255.0f * 2.0f;

            TGAReadPixel(srcImage, width, bpp / 8, &pix, (x + 1) % width, (y + 1) % height);
            dX += ((float)pix.red) / 255.0f * 1.0f;

            // Cross Product of components of gradient reduces to
            float nX = -dX;
            float nY = -dY;
            float nZ = 1;

            // Normalize
            float oolen = 1.0f / ((float)sqrt(nX * nX + nY * nY + nZ * nZ));
            nX *= oolen;
            nY *= oolen;
            nZ *= oolen;

            pix.red = (uint8)PackFloatInByte(nX);
            pix.green = (uint8)PackFloatInByte(nY);
            pix.blue = (uint8)PackFloatInByte(nZ);
            pix.alpha = 255;
            pix.red = 128;

            WritePixel(dstImage, bpp, &pix, x, y);
        }
    }
}

int main(int argc, const char* argv[])
{
    auto src = LoadPixmap("https://github.com/UltraEngine/Documentation/raw/master/Assets/Materials/Brick/brickwall01.dds");
    if (src->format != TEXTURE_BGRA) src = src->Convert(TEXTURE_BGRA);
    
    auto dest = CreatePixmap(src->size.x, src->size.y, src->format);
    
    SobelFilter((uint8*)dest->pixels->Data(), (uint8*)src->pixels->Data(), src->size.x, src->size.y, 32);

    src->Save(GetPath(PATH_DESKTOP) + "/test.dds");
    dest->Save(GetPath(PATH_DESKTOP) + "/testDOT3.dds");

    return 0;
}

Input

Output