Using SDL to generate images with dart and isolates.

main.dart

import 'dart:ffi';
import 'dart:io';
import 'dart:math';

import 'package:ffi/ffi.dart';
import 'package:sdl2/sdl2.dart';

class FontData {
  FontData(this.fontSource, this.fontSize);

  final String fontSource;
  final int fontSize;
}

int exportImages(List<String> texts, int outputNumber, bool premium) {
  final fontData = FontData('assets/fonts/ALS-Script.ttf', 148);

  for (var i = 0; i < texts.length; i++) {
    while (texts[0].contains('  ')) {
      texts[0] = texts[0].replaceAll(RegExp(r'\s{2,}'), ' ');
    }
  }

  final outputDir = 'outputs_KMO$outputNumber';

  final cert = {true: 'cert_premium', false: 'cert_normal'};

  final backgroundPath = 'assets/${cert[premium]}.jpg';

  final img = imgLoad(backgroundPath);

  if (img == nullptr) {
    return -1;
  }

  final window = sdlCreateWindow(
      'Render Certs_${texts[0]}',
      SDL_WINDOWPOS_UNDEFINED,
      SDL_WINDOWPOS_UNDEFINED,
      img.ref.w,
      img.ref.h,
      SDL_WINDOW_HIDDEN);

  for (var i = 0; i < texts.length; i++) {
    final name = texts[i];
    renderImage(window, img, fontData, name,
        '$outputDir${Platform.pathSeparator}$name.jpg', premium);
  }

  sdlFreeSurface(img);
  sdlDestroyWindow(window);

  return 0;
}

void renderImage(Pointer<SdlWindow> window, Pointer<SdlSurface> img,
    FontData fontData, String text, String output, bool premium) {
  final renderer = sdlCreateRenderer(
      window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_TARGETTEXTURE);
  final tImg = sdlCreateTextureFromSurface(renderer, img);

  final zw = calloc<Int32>()..value = 0;
  final zh = calloc<Int32>()..value = 0;

  sdlQueryTexture(tImg, nullptr, nullptr, zw, zh);

  final dstRect =
      Rectangle<double>(0, 0, zw.value.toDouble(), zh.value.toDouble());
  final dstRectPointer = dstRect.calloc();

  sdlRenderCopy(renderer, tImg, nullptr, dstRectPointer);

  var surface = sdlCreateRgbSurfaceWithFormat(
      0, img.ref.w, img.ref.h, 32, SDL_PIXELFORMAT_RGBA8888);

  sdlRenderReadPixels(
    renderer,
    nullptr,
    surface.ref.format.ref.format,
    surface.ref.pixels,
    surface.ref.pitch,
  );

  renderText(renderer, fontData, text, premium);

  sdlRenderReadPixels(
    renderer,
    nullptr,
    surface.ref.format.ref.format,
    surface.ref.pixels,
    surface.ref.pitch,
  );

  zw.callocFree();
  zh.callocFree();
  imgSaveJpg(surface, output, 99);
  sdlDestroyTexture(tImg);
  sdlFreeSurface(surface);
  sdlDestroyRenderer(renderer);
}

void renderText(Pointer<SdlRenderer> renderer, FontData fontData, String text,
    bool premium) {
  var font = ttfOpenFont(fontData.fontSource, fontData.fontSize);
  ttfSetFontHinting(font, TTF_HINTING_NORMAL);
  final color = premium ? hexToRGBA('000000FF') : hexToRGBA('38241BFF');

  final zw = calloc<Int32>()..value = 0;
  final zh = calloc<Int32>()..value = 0;

  final textWidth = calloc<Int32>()..value = 0;
  final textHeight = calloc<Int32>()..value = 0;
  ttfSizeText(font, text, textWidth, textHeight);

  var newFontSize = fontData.fontSize;
  const textMaxHeight = 150;
  while (textHeight.value > textMaxHeight) {
    newFontSize -= 1;
    font = ttfOpenFont(fontData.fontSource, newFontSize);
    ttfSizeText(font, text, textWidth, textHeight);
  }

  final leftMargin = premium ? 300 : 187;
  final rightMargin = premium ? 300 : 187;

  final imgWid = premium ? 2000 : 2339;

  final textMaxWidth = imgWid - leftMargin - rightMargin;
  var newRectW = textWidth;
  var newRectH = textHeight;

  if (newRectW.value > textMaxWidth) {
    newRectH.value = textHeight.value * textMaxWidth ~/ textWidth.value;
    newRectW.value = textWidth.value * textMaxWidth ~/ textWidth.value;
  }

  final tSurf = ttfRenderTextBlendedWrapped(font, text,
      (calloc<SdlColor>()..setRgba(color.r, color.g, color.b, color.a)).ref, 0);

  final tText = sdlCreateTextureFromSurface(renderer, tSurf);

  final topMargin =
      (premium ? 660 : 840) + (textMaxHeight - newRectH.value) / 2;

  sdlQueryTexture(tText, nullptr, nullptr, zw, zh);
  final dstRect = Rectangle<double>(imgWid / 2 - newRectW.value / 2, topMargin,
          newRectW.value.toDouble(), newRectH.value.toDouble())
      .calloc();
  sdlRenderCopy(renderer, tText, nullptr, dstRect);
  sdlDestroyTexture(tText);
  sdlFreeSurface(tSurf);
}

class RGBA {
  final int r;
  final int g;
  final int b;
  final int a;

  RGBA(this.r, this.g, this.b, this.a);

  @override
  String toString() {
    return 'RGBA($r, $g, $b, $a)';
  }
}

RGBA hexToRGBA(String hexColor) {
  hexColor = hexColor.toUpperCase().replaceAll("#", "");
  if (hexColor.length == 6) {
    hexColor = "FF$hexColor";
  }
  int hexVal = int.parse(hexColor, radix: 16);
  return RGBA(
    (hexVal >> 24) & 255,
    (hexVal >> 16) & 255,
    (hexVal >> 8) & 255,
    hexVal & 255,
  );
}

sdl_gen.dart

import 'dart:ffi';
import 'dart:io';
import 'dart:math';

import 'package:ffi/ffi.dart';
import 'package:sdl2/sdl2.dart';

class FontData {
  FontData(this.fontSource, this.fontSize);

  final String fontSource;
  final int fontSize;
}

int exportImages(List<String> texts, int outputNumber, bool premium) {
  final fontData = FontData('assets/fonts/ALS-Script.ttf', 148);

  for (var i = 0; i < texts.length; i++) {
    while (texts[0].contains('  ')) {
      texts[0] = texts[0].replaceAll(RegExp(r'\s{2,}'), ' ');
    }
  }

  final outputDir = 'outputs_KMO$outputNumber';

  final cert = {true: 'cert_premium', false: 'cert_normal'};

  final backgroundPath = 'assets/${cert[premium]}.jpg';

  final img = imgLoad(backgroundPath);

  if (img == nullptr) {
    return -1;
  }

  final window = sdlCreateWindow(
      'Render Certs_${texts[0]}',
      SDL_WINDOWPOS_UNDEFINED,
      SDL_WINDOWPOS_UNDEFINED,
      img.ref.w,
      img.ref.h,
      SDL_WINDOW_HIDDEN);

  for (var i = 0; i < texts.length; i++) {
    final name = texts[i];
    renderImage(window, img, fontData, name,
        '$outputDir${Platform.pathSeparator}$name.jpg', premium);
  }

  sdlFreeSurface(img);
  sdlDestroyWindow(window);

  return 0;
}

void renderImage(Pointer<SdlWindow> window, Pointer<SdlSurface> img,
    FontData fontData, String text, String output, bool premium) {
  final renderer = sdlCreateRenderer(
      window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_TARGETTEXTURE);
  final tImg = sdlCreateTextureFromSurface(renderer, img);

  final zw = calloc<Int32>()..value = 0;
  final zh = calloc<Int32>()..value = 0;

  sdlQueryTexture(tImg, nullptr, nullptr, zw, zh);

  final dstRect =
      Rectangle<double>(0, 0, zw.value.toDouble(), zh.value.toDouble());
  final dstRectPointer = dstRect.calloc();

  sdlRenderCopy(renderer, tImg, nullptr, dstRectPointer);

  var surface = sdlCreateRgbSurfaceWithFormat(
      0, img.ref.w, img.ref.h, 32, SDL_PIXELFORMAT_RGBA8888);

  sdlRenderReadPixels(
    renderer,
    nullptr,
    surface.ref.format.ref.format,
    surface.ref.pixels,
    surface.ref.pitch,
  );

  renderText(renderer, fontData, text, premium);

  sdlRenderReadPixels(
    renderer,
    nullptr,
    surface.ref.format.ref.format,
    surface.ref.pixels,
    surface.ref.pitch,
  );

  zw.callocFree();
  zh.callocFree();
  imgSaveJpg(surface, output, 99);
  sdlDestroyTexture(tImg);
  sdlFreeSurface(surface);
  sdlDestroyRenderer(renderer);
}

void renderText(Pointer<SdlRenderer> renderer, FontData fontData, String text,
    bool premium) {
  var font = ttfOpenFont(fontData.fontSource, fontData.fontSize);
  ttfSetFontHinting(font, TTF_HINTING_NORMAL);
  final color = premium ? hexToRGBA('000000FF') : hexToRGBA('38241BFF');

  final zw = calloc<Int32>()..value = 0;
  final zh = calloc<Int32>()..value = 0;

  final textWidth = calloc<Int32>()..value = 0;
  final textHeight = calloc<Int32>()..value = 0;
  ttfSizeText(font, text, textWidth, textHeight);

  var newFontSize = fontData.fontSize;
  const textMaxHeight = 150;
  while (textHeight.value > textMaxHeight) {
    newFontSize -= 1;
    font = ttfOpenFont(fontData.fontSource, newFontSize);
    ttfSizeText(font, text, textWidth, textHeight);
  }

  final leftMargin = premium ? 300 : 187;
  final rightMargin = premium ? 300 : 187;

  final imgWid = premium ? 2000 : 2339;

  final textMaxWidth = imgWid - leftMargin - rightMargin;
  var newRectW = textWidth;
  var newRectH = textHeight;

  if (newRectW.value > textMaxWidth) {
    newRectH.value = textHeight.value * textMaxWidth ~/ textWidth.value;
    newRectW.value = textWidth.value * textMaxWidth ~/ textWidth.value;
  }

  final tSurf = ttfRenderTextBlendedWrapped(font, text,
      (calloc<SdlColor>()..setRgba(color.r, color.g, color.b, color.a)).ref, 0);

  final tText = sdlCreateTextureFromSurface(renderer, tSurf);

  final topMargin =
      (premium ? 660 : 840) + (textMaxHeight - newRectH.value) / 2;

  sdlQueryTexture(tText, nullptr, nullptr, zw, zh);
  final dstRect = Rectangle<double>(imgWid / 2 - newRectW.value / 2, topMargin,
          newRectW.value.toDouble(), newRectH.value.toDouble())
      .calloc();
  sdlRenderCopy(renderer, tText, nullptr, dstRect);
  sdlDestroyTexture(tText);
  sdlFreeSurface(tSurf);
}

class RGBA {
  final int r;
  final int g;
  final int b;
  final int a;

  RGBA(this.r, this.g, this.b, this.a);

  @override
  String toString() {
    return 'RGBA($r, $g, $b, $a)';
  }
}

RGBA hexToRGBA(String hexColor) {
  hexColor = hexColor.toUpperCase().replaceAll("#", "");
  if (hexColor.length == 6) {
    hexColor = "FF$hexColor";
  }
  int hexVal = int.parse(hexColor, radix: 16);
  return RGBA(
    (hexVal >> 24) & 255,
    (hexVal >> 16) & 255,
    (hexVal >> 8) & 255,
    hexVal & 255,
  );
}