clay/renderers/GLES3/clay_renderer_gles3_loader_stb.c

#pragma once

#include <stdbool.h>
#include <clay.h>

#include <stb_image.h>
#include <stb_truetype.h>

#include "clay_renderer_gles3.h"

typedef struct LoadedImage
{
    unsigned char *data;
    int width;
    int height;
    int channels;
} LoadedImage;

typedef struct LoadedImageInternal
{
    LoadedImage pub;
} LoadedImageInternal;

static LoadedImageInternal g_imageSlot;

const LoadedImage *loadImage(const char *path, bool flip)
{
    if (!path)
        return NULL;

    stbi_set_flip_vertically_on_load(flip ? 1 : 0);

    int w = 0;
    int h = 0;
    int c = 0;

    unsigned char *data = stbi_load(path, &w, &h, &c, 0);
    if (!data)
    {
        // Failed
        g_imageSlot.pub.data = NULL;
        g_imageSlot.pub.width = 0;
        g_imageSlot.pub.height = 0;
        g_imageSlot.pub.channels = 0;
        return NULL;
    }

    g_imageSlot.pub.data = data;
    g_imageSlot.pub.width = w;
    g_imageSlot.pub.height = h;
    g_imageSlot.pub.channels = c;

    return &g_imageSlot.pub;
}

void freeImage(const LoadedImage *img)
{
    if (!img || !img->data)
        return;

    // cast back to internal container
    stbi_image_free((void *)img->data);

    // reset slot
    g_imageSlot.pub.data = NULL;
    g_imageSlot.pub.width = 0;
    g_imageSlot.pub.height = 0;
    g_imageSlot.pub.channels = 0;
}

typedef struct Stb_FontData
{
    float bakePxH;   // font baking height (e.g. 48.0f)
    float ascentPx;  // in baked pixels (at bake_px size)
    float descentPx; // usually negative (at bake_px size)
    int firstChar;   // e.g. 32
    int charCount;   // e.g. 96
    stbtt_bakedchar *cdata;
    int atlasW;
    int atlasH;
} Stb_FontData;

bool Stb_LoadFont(
    GLuint *textureOut,
    Stb_FontData *fontOut,
    const char *ttfPath,
    float bakePxH, // Height of a char in pixels
    int atlasW,    // Width of atlas in pixels
    int atlasH     // Height of atlas in pixels
)
{
    fontOut->firstChar = 32; // ASCII space
    fontOut->charCount = 96; // 32..127
    fontOut->bakePxH = bakePxH;
    fontOut->atlasW = atlasW;
    fontOut->atlasH = atlasH;

    // allocate baked-char array
    fontOut->cdata = (stbtt_bakedchar *)malloc(
        sizeof(stbtt_bakedchar) // Store baked info
        * fontOut->charCount    // For each char
    );
    if (!fontOut->cdata)
    {
        fprintf(stderr, "Cannot allocate cdata\n");
        return false;
    }

    FILE *f = fopen(ttfPath, "rb");
    if (!f)
    {
        fprintf(stderr, "Could not open font: %s\n", ttfPath);
        return false;
    }

    fseek(f, 0, SEEK_END);
    long sz = ftell(f);
    fseek(f, 0, SEEK_SET);

    unsigned char *ttf_buf = (unsigned char *)malloc(sz);
    fread(ttf_buf, 1, sz, f);
    fclose(f);

    // temporary atlas memory
    unsigned char *atlas = (unsigned char *)malloc(atlasW * atlasH);
    memset(atlas, 0, atlasW * atlasH);

    // bake
    int res = stbtt_BakeFontBitmap(
        ttf_buf,            // raw TTF file
        0,                  // font index inside TTF (0 = first font)
        bakePxH,            // pixel height of glyphs to generate
        atlas,              // OUT: bitmap buffer (unsigned char*)
        atlasW, atlasH,     // size of bitmap buffer
        fontOut->firstChar, // first character to bake (e.g., 32 = space)
        fontOut->charCount, // how many sequential chars to bake
        fontOut->cdata      // OUT: array of stbtt_bakedchar
    );

    stbtt_fontinfo fi;
    if (!stbtt_InitFont(&fi, ttf_buf, stbtt_GetFontOffsetForIndex(ttf_buf, 0)))
    {
        return false;
    }

    int ascent, descent, lineGap;
    stbtt_GetFontVMetrics(&fi, &ascent, &descent, &lineGap);

    // Convert the font's "font units" to pixels proportional to bakePxH size:
    float scaleForBake = stbtt_ScaleForPixelHeight(&fi, bakePxH);

    fontOut->ascentPx = ascent * scaleForBake;
    fontOut->descentPx = descent * scaleForBake; // this is typically negative

    free(ttf_buf);

    if (res <= 0)
    {
        fprintf(stderr, "Font baking failed\n");
        free(atlas);
        free(fontOut->cdata);
        fontOut->cdata = NULL;
        return false;
    }

    // Creating glyphVtxArray atlas texture
    glGenTextures(1, textureOut);
    glBindTexture(GL_TEXTURE_2D, *textureOut);

    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

    glTexImage2D(GL_TEXTURE_2D, 0, GL_R8,
                 atlasW, atlasH,
                 0, GL_RED, GL_UNSIGNED_BYTE, atlas);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    glBindTexture(GL_TEXTURE_2D, 0);

    free(atlas);

    return true;
}

static inline Clay_Dimensions Stb_MeasureText(
    Clay_StringSlice glyphVtxArray,
    Clay_TextElementConfig *config,
    void *userData)
{
    Stb_FontData *fontData = (Stb_FontData *)userData;

    if (!fontData->cdata)
    {
        fprintf(
            stderr,
            "MeasureText cannot do anything when cdata is not baked: '%.*s' → %d x %d px\n",
            (int)glyphVtxArray.length, glyphVtxArray.chars, 0, 0);
        return (Clay_Dimensions){.width = 0, .height = 0};
    }

    float x = 0.0f;
    float y = 0.0f;

    const char *str = glyphVtxArray.chars;
    int len = glyphVtxArray.length;

    float scale = config->fontSize / fontData->bakePxH;

    float letterSpacing = (float)config->letterSpacing;
    float lineHeight = (config->lineHeight > 0)
                           ? (float)config->lineHeight
                           : fontData->bakePxH;

    for (int i = 0; i < len; i++)
    {
        unsigned char c = str[i];

        if (c < fontData->firstChar                           // before range
            || c >= fontData->firstChar + fontData->charCount // after range
        )
        {
            // Unsupported char: treat as space
            fprintf(stderr, "illegal char %d\n", (int)c);
            x += fontData->bakePxH * 0.25f;
            continue;
        }

        stbtt_bakedchar *b = &fontData->cdata[c - fontData->firstChar];

        // horizontal advance while moving along word characters
        x += b->xadvance * scale + letterSpacing;
    }

    float ascent = fontData->ascentPx * scale;
    float descent = fontData->descentPx * scale; // negative
    float lineH = (ascent - descent);            // total line height in pixels (at requested fontSize)

    return (Clay_Dimensions){
        .width = x,
        .height = y + lineH,
    };
}

static inline void Stb_RenderText(
    Clay_RenderCommand *cmd,
    Gles3_GlyphVtxArray *glyphVtxArray,
    void *userData)
{
    const Clay_TextRenderData *tr = &cmd->renderData.text;

    float cr = tr->textColor.r / 255.0f;
    float cg = tr->textColor.g / 255.0f;
    float cb = tr->textColor.b / 255.0f;
    float ca = tr->textColor.a / 255.0f;
    float fontToUse = (float)tr->fontId;

    Stb_FontData *fontArray = (Stb_FontData *)userData;
    Stb_FontData *stbFontData = &fontArray[tr->fontId];
    if (!stbFontData->cdata)
        return;

    Clay_StringSlice ss = tr->stringContents;
    const char *txt = ss.chars;
    int len = (int)ss.length;

    float scale = tr->fontSize / stbFontData->bakePxH;
    float ascent = stbFontData->ascentPx * scale; // pixels above baseline
    float x = cmd->boundingBox.x;
    float y = cmd->boundingBox.y + ascent; // baseline (note: no descent)

    for (int i = 0; i < len; i++)
    {
        char ch = txt[i];

        int idx = ch - stbFontData->firstChar;
        if (idx < 0 || idx >= stbFontData->charCount)
        {
            continue;
        }

        stbtt_bakedchar *bc = &stbFontData->cdata[idx];

        float gw = (float)(bc->x1 - bc->x0); // glyph width in atlas pixels
        float gh = (float)(bc->y1 - bc->y0); // glyph height

        float sw = gw * scale; // scaled width on screen
        float sh = gh * scale; // scaled height

        float ox = bc->xoff * scale; // baseline offset
        float oy = bc->yoff * scale;

        // top-left corner on screen (pixel coords)
        float x0 = x + ox;
        float y0 = y + oy;
        float x1 = x0 + sw;
        float y1 = y0 + sh;

        // atlas size (you can make it configurable later)
        float atlasW = stbFontData->atlasW;
        float atlasH = stbFontData->atlasH;

        float u0 = bc->x0 / atlasW;
        float v0 = bc->y0 / atlasH;
        float u1 = bc->x1 / atlasW;
        float v1 = bc->y1 / atlasH;

        // append 6 vertices (two triangles) to your buffer
        GlyphVtx *v = &glyphVtxArray->instData[glyphVtxArray->count * 6];

        v[0] = (GlyphVtx){x0, y0, u0, v0, cr, cg, cb, ca, fontToUse};
        v[1] = (GlyphVtx){x1, y0, u1, v0, cr, cg, cb, ca, fontToUse};
        v[2] = (GlyphVtx){x0, y1, u0, v1, cr, cg, cb, ca, fontToUse};

        v[3] = (GlyphVtx){x0, y1, u0, v1, cr, cg, cb, ca, fontToUse};
        v[4] = (GlyphVtx){x1, y0, u1, v0, cr, cg, cb, ca, fontToUse};
        v[5] = (GlyphVtx){x1, y1, u1, v1, cr, cg, cb, ca, fontToUse};

        // advance pen by baked xadvance + letter spacing
        x += (bc->xadvance * scale) + tr->letterSpacing;

        // prevent buffer overrun
        if (glyphVtxArray->count >= glyphVtxArray->capacity)
        {
            break;
        }
        glyphVtxArray->count++;
    }
}

bool Stb_LoadImage(GLuint *textureOut, const char *path)
{
    const LoadedImage *li = loadImage(path, false);
    if (!li || !li->data)
    {
        fprintf(stderr, "Failed to load texture at: %s\n", path);
        return false;
    }

    glGenTextures(1, textureOut);
    glBindTexture(GL_TEXTURE_2D, *textureOut);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

    GLenum format = (li->channels == 4) ? GL_RGBA : GL_RGB;

    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

    glTexImage2D(
        GL_TEXTURE_2D, // target
        0,             // level
        format,        // internal format int
        li->width,
        li->height,
        0,                // border
        format,           // format, GLEnum
        GL_UNSIGNED_BYTE, // Type
        li->data          // pixels
    );

    glGenerateMipmap(GL_TEXTURE_2D);

    freeImage(li);
    return true;
}