Adds color space to textures.

PiperOrigin-RevId: 761907261
Change-Id: Iec546d1d5907a15e57ef809ec31850640fc52915

src/user/user_objects.cc

@@ -55,6 +55,8 @@ class PNGImage {
                        LodePNGColorType color_type);
   int Width() const { return width_; }
   int Height() const { return height_; }
+  bool IsSRGB() const { return is_srgb_; }
+
   uint8_t operator[] (int i) const { return data_[i]; }
   std::vector<unsigned char>& MoveData() { return data_; }
 
@@ -65,6 +67,7 @@ class PNGImage {
 
   int width_;
   int height_;
+  bool is_srgb_;
   LodePNGColorType color_type_;
   std::vector<uint8_t> data_;
 };
@@ -104,8 +107,11 @@ PNGImage PNGImage::Load(const mjCBase* obj, mjResource* resource,
 
   // decode PNG from buffer
   unsigned int w, h;
-  unsigned err = lodepng::decode(image.data_, w, h,
-                                 buffer, nbuffer, image.color_type_, 8);
+
+  lodepng::State state;
+  state.info_raw.colortype = image.color_type_;
+  state.info_raw.bitdepth = 8;
+  unsigned err = lodepng::decode(image.data_, w, h, state, buffer, nbuffer);
 
   // check for errors
   if (err) {
@@ -116,6 +122,7 @@ PNGImage PNGImage::Load(const mjCBase* obj, mjResource* resource,
 
   image.width_ = w;
   image.height_ = h;
+  image.is_srgb_ = (state.info_png.srgb_defined == 1);
 
   if (image.width_ <= 0 || image.height_ < 0) {
     std::stringstream ss;
@@ -4257,7 +4264,7 @@ void mjCTexture::BuiltinCube(void) {
 // load PNG file
 void mjCTexture::LoadPNG(mjResource* resource,
                          std::vector<unsigned char>& image,
-                         unsigned int& w, unsigned int& h) {
+                         unsigned int& w, unsigned int& h, bool& is_srgb) {
   LodePNGColorType color_type;
   if (nchannel == 4) {
     color_type = LCT_RGBA;
@@ -4272,13 +4279,14 @@ void mjCTexture::LoadPNG(mjResource* resource,
   PNGImage png_image = PNGImage::Load(this, resource, color_type);
   w = png_image.Width();
   h = png_image.Height();
+  is_srgb = png_image.IsSRGB();
   image = png_image.MoveData();
 }
 
 // load custom file
 void mjCTexture::LoadCustom(mjResource* resource,
                             std::vector<unsigned char>& image,
-                            unsigned int& w, unsigned int& h) {
+                            unsigned int& w, unsigned int& h, bool& is_srgb) {
   const void* buffer = 0;
   int buffer_sz = mju_readResource(resource, &buffer);
 
@@ -4295,6 +4303,9 @@ void mjCTexture::LoadCustom(mjResource* resource,
   w = pint[0];
   h = pint[1];
 
+  // assume linear color space
+  is_srgb = false;
+
   // check dimensions
   if (w < 1 || h < 1) {
     throw mjCError(this, "Non-PNG texture, assuming custom binary file format,\n"
@@ -4317,7 +4328,7 @@ void mjCTexture::LoadCustom(mjResource* resource,
 // load from PNG or custom file, flip if specified
 void mjCTexture::LoadFlip(std::string filename, const mjVFS* vfs,
                           std::vector<unsigned char>& image,
-                          unsigned int& w, unsigned int& h) {
+                          unsigned int& w, unsigned int& h, bool& is_srgb) {
   std::string asset_type = GetAssetContentType(filename, content_type_);
 
   // fallback to custom
@@ -4333,9 +4344,9 @@ void mjCTexture::LoadFlip(std::string filename, const mjVFS* vfs,
 
   try {
     if (asset_type == "image/png") {
-      LoadPNG(resource, image, w, h);
+      LoadPNG(resource, image, w, h, is_srgb);
     } else {
-      LoadCustom(resource, image, w, h);
+      LoadCustom(resource, image, w, h, is_srgb);
     }
     mju_closeResource(resource);
   } catch(mjCError err) {
@@ -4402,12 +4413,16 @@ void mjCTexture::LoadFlip(std::string filename, const mjVFS* vfs,
 void mjCTexture::Load2D(std::string filename, const mjVFS* vfs) {
   // load PNG or custom
   unsigned int w, h;
+  bool is_srgb;
   std::vector<unsigned char> image;
-  LoadFlip(filename, vfs, image, w, h);
+  LoadFlip(filename, vfs, image, w, h, is_srgb);
 
   // assign size
   width = w;
   height = h;
+  if (colorspace == mjCOLORSPACE_AUTO) {
+    colorspace = is_srgb ? mjCOLORSPACE_SRGB : mjCOLORSPACE_LINEAR;
+  }
 
   // allocate and copy data
   std::int64_t size = static_cast<std::int64_t>(width)*height;
@@ -4435,8 +4450,13 @@ void mjCTexture::LoadCubeSingle(std::string filename, const mjVFS* vfs) {
 
   // load PNG or custom
   unsigned int w, h;
+  bool is_srgb;
   std::vector<unsigned char> image;
-  LoadFlip(filename, vfs, image, w, h);
+  LoadFlip(filename, vfs, image, w, h, is_srgb);
+
+  if (colorspace == mjCOLORSPACE_AUTO) {
+    colorspace = is_srgb ? mjCOLORSPACE_SRGB : mjCOLORSPACE_LINEAR;
+  }
 
   // check gridsize for compatibility
   if (w/gridsize[1] != h/gridsize[0] || (w%gridsize[1]) || (h%gridsize[0])) {
@@ -4549,8 +4569,14 @@ void mjCTexture::LoadCubeSeparate(const mjVFS* vfs) {
 
       // load PNG or custom
       unsigned int w, h;
+      bool is_srgb;
       std::vector<unsigned char> image;
-      LoadFlip(filename.Str(), vfs, image, w, h);
+      LoadFlip(filename.Str(), vfs, image, w, h, is_srgb);
+
+      // assume all faces have the same colorspace
+      if (colorspace == mjCOLORSPACE_AUTO) {
+        colorspace = is_srgb ? mjCOLORSPACE_SRGB : mjCOLORSPACE_LINEAR;
+      }
 
       // PNG must be square
       if (w != h) {