Web Screenshots

lib/aux_js.cpp

@@ -9,21 +9,34 @@
 // terms of the BSD-3 license. We welcome feedback and contributions, see file
 // CONTRIBUTING.md for details.
 
-#include "visual.hpp"
+#include "aux_vis.hpp"
 #include "palettes.hpp"
 #include "stream_reader.hpp"
+#include "visual.hpp"
+
+#ifdef GLVIS_USE_LIBPNG
+#include <png.h>
+#endif
+
 #include <SDL2/SDL_hints.h>
 #include <emscripten/bind.h>
 #include <emscripten/html5.h>
+#include <emscripten/val.h>
 
 // used in extern context
 thread_local std::string plot_caption;
 thread_local std::string extra_caption;
 thread_local mfem::GeometryRefiner GLVisGeometryRefiner;
 
 static VisualizationSceneScalarData * vs = nullptr;
+
+// either bitmap data or png bytes
+std::vector<unsigned char> * screen_state = nullptr;
+
 StreamState stream_state;
 
+namespace em = emscripten;
+
 namespace js
 {
 
@@ -311,11 +324,93 @@ std::string getHelpString()
       = dynamic_cast<VisualizationSceneScalarData*>(GetVisualizationScene());
    return vss->GetHelpString();
 }
+
+em::val getScreenBuffer(bool flip_y=false)
+{
+   MyExpose();
+   auto * wnd = GetAppWindow();
+   int w, h;
+   wnd->getGLDrawSize(w, h);
+
+   // 4 bytes for rgba
+   const size_t buffer_size = w*h*4;
+   if (screen_state == nullptr)
+   {
+      screen_state = new std::vector<unsigned char>(buffer_size);
+   }
+   else if (buffer_size > screen_state->size())
+   {
+      screen_state->resize(buffer_size);
+   }
+
+   glReadPixels(0, 0, w, h, GL_RGBA, GL_UNSIGNED_BYTE, screen_state->data());
+
+   // `canvas` starts at top left but `glReadPixels' starts at bottom left
+   if (flip_y)
+   {
+      auto * orig = screen_state;
+      auto * flip = new std::vector<unsigned char>(buffer_size);
+      // from `glReadPixels` man page: Pixels are returned in row order from
+      // the lowest to the highest row, left to right in each row.
+      for (int j = 0; j < h; ++j)
+      {
+         for (int i = 0; i < w*4; ++i)
+         {
+            (*flip)[4*w*j + i] = (*orig)[4*w*(h-j-1) + i];
+         }
+      }
+      screen_state = flip;
+      delete orig;
+   }
+
+   return em::val(em::typed_memory_view(screen_state->size(),
+                                        screen_state->data()));
+}
+
+#ifdef GLVIS_USE_LIBPNG
+em::val getPNGByteArray()
+{
+   constexpr const char * filename = "im.png";
+   auto * wnd = GetAppWindow();
+   int w, h;
+   wnd->getGLDrawSize(w, h);
+
+   MyExpose();
+   // save to in-memory file
+   int status = SaveAsPNG(filename, w, h, wnd->isHighDpi(), true);
+   if (status != 0)
+   {
+      fprintf(stderr, "unable to generate png\n");
+      return em::val::null();
+   }
+
+   // load in-memory file to byte array
+   std::ifstream ifs(filename, std::ios::binary);
+   if (!ifs)
+   {
+      fprintf(stderr, "unable to load png\n");
+      return em::val::null();
+   }
+
+   if (!screen_state)
+   {
+      screen_state = new std::vector<unsigned char>(std::istreambuf_iterator<char>
+                                                    (ifs), {});
+   }
+   else
+   {
+      screen_state->assign(std::istreambuf_iterator<char>
+                           (ifs), {});
+   }
+
+   return em::val(em::typed_memory_view(screen_state->size(),
+                                        screen_state->data()));
+}
+#endif // GLVIS_USE_LIBPNG
 } // namespace js
 
 // Info on type conversion:
 // https://emscripten.org/docs/porting/connecting_cpp_and_javascript/embind.html#built-in-type-conversions
-namespace em = emscripten;
 EMSCRIPTEN_BINDINGS(js_funcs)
 {
    em::function("startVisualization", &js::startVisualization);
@@ -334,4 +429,8 @@ EMSCRIPTEN_BINDINGS(js_funcs)
    em::function("getHelpString", &js::getHelpString);
    em::function("processKeys", &js::processKeys);
    em::function("processKey", &js::processKey);
+   em::function("getScreenBuffer", &js::getScreenBuffer);
+#ifdef GLVIS_USE_LIBPNG
+   em::function("getPNGByteArray", &js::getPNGByteArray);
+#endif
 }

lib/aux_vis.cpp

@@ -890,6 +890,74 @@ int InvertSurfaceVertical(SDL_Surface *surface)
    return 0;
 }
 
+#ifdef GLVIS_USE_LIBPNG
+int SaveAsPNG(const char *fname, int w, int h, bool is_hidpi, bool with_alpha)
+{
+   png_byte *pixels = new png_byte[(with_alpha ? 4 : 3)*w];
+   if (!pixels)
+   {
+      return 1;
+   }
+
+   png_structp png_ptr =
+      png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
+   if (!png_ptr)
+   {
+      delete [] pixels;
+      return 1;
+   }
+   png_infop info_ptr = png_create_info_struct(png_ptr);
+   if (!info_ptr)
+   {
+      png_destroy_write_struct(&png_ptr, (png_infopp)NULL);
+      delete [] pixels;
+      return 1;
+   }
+
+   FILE *fp = fopen(fname, "wb");
+   if (!fp)
+   {
+      png_destroy_write_struct(&png_ptr, &info_ptr);
+      delete [] pixels;
+      return 2;
+   }
+
+   if (setjmp(png_jmpbuf(png_ptr)))
+   {
+      fclose(fp);
+      png_destroy_write_struct(&png_ptr, &info_ptr);
+      delete [] pixels;
+      return 3;
+   }
+
+   png_uint_32 ppi = is_hidpi ? 144 : 72; // pixels/inch
+   png_uint_32 ppm = ppi/0.0254 + 0.5;            // pixels/meter
+   png_set_pHYs(png_ptr, info_ptr, ppm, ppm, PNG_RESOLUTION_METER);
+
+   png_init_io(png_ptr, fp);
+   png_set_IHDR(png_ptr, info_ptr, w, h, 8,
+                with_alpha ? PNG_COLOR_TYPE_RGBA : PNG_COLOR_TYPE_RGB,
+                PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT,
+                PNG_FILTER_TYPE_DEFAULT);
+
+
+   png_write_info(png_ptr, info_ptr);
+   for (int i = 0; i < h; i++)
+   {
+      glReadPixels(0, h-1-i, w, 1, with_alpha ? GL_RGBA : GL_RGB, GL_UNSIGNED_BYTE,
+                   pixels);
+      png_write_row(png_ptr, pixels);
+   }
+   png_write_end(png_ptr, info_ptr);
+
+   fclose(fp);
+   png_destroy_write_struct(&png_ptr, &info_ptr);
+   delete [] pixels;
+
+   return 0;
+}
+#endif // GLVIS_USE_LIBPNG
+
 int Screenshot(const char *fname, bool convert)
 {
 #ifdef GLVIS_DEBUG
@@ -987,64 +1055,8 @@ int Screenshot(const char *fname, bool convert)
 
 #elif defined(GLVIS_USE_LIBPNG)
    // Save as png image. Requires libpng.
-
-   png_byte *pixels = new png_byte[3*w];
-   if (!pixels)
-   {
-      return 1;
-   }
-
-   png_structp png_ptr =
-      png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
-   if (!png_ptr)
-   {
-      delete [] pixels;
-      return 1;
-   }
-   png_infop info_ptr = png_create_info_struct(png_ptr);
-   if (!info_ptr)
-   {
-      png_destroy_write_struct(&png_ptr, (png_infopp)NULL);
-      delete [] pixels;
-      return 1;
-   }
-
-   FILE *fp = fopen(filename.c_str(), "wb");
-   if (!fp)
-   {
-      png_destroy_write_struct(&png_ptr, &info_ptr);
-      delete [] pixels;
-      return 2;
-   }
-
-   if (setjmp(png_jmpbuf(png_ptr)))
-   {
-      fclose(fp);
-      png_destroy_write_struct(&png_ptr, &info_ptr);
-      delete [] pixels;
-      return 3;
-   }
-
-   png_uint_32 ppi = wnd->isHighDpi() ? 144 : 72; // pixels/inch
-   png_uint_32 ppm = ppi/0.0254 + 0.5;            // pixels/meter
-   png_set_pHYs(png_ptr, info_ptr, ppm, ppm, PNG_RESOLUTION_METER);
-
-   png_init_io(png_ptr, fp);
-   png_set_IHDR(png_ptr, info_ptr, w, h, 8, PNG_COLOR_TYPE_RGB,
-                PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT,
-                PNG_FILTER_TYPE_DEFAULT);
-
-   png_write_info(png_ptr, info_ptr);
-   for (int i = 0; i < h; i++)
-   {
-      glReadPixels(0, h-1-i, w, 1, GL_RGB, GL_UNSIGNED_BYTE, pixels);
-      png_write_row(png_ptr, pixels);
-   }
-   png_write_end(png_ptr, info_ptr);
-
-   fclose(fp);
-   png_destroy_write_struct(&png_ptr, &info_ptr);
-   delete [] pixels;
+   int status = SaveAsPNG(filename.c_str(), w, h, wnd->isHighDpi());
+   if (status != 0) { return status; }
 
 #else
    // use SDL for screenshots

lib/aux_vis.hpp

@@ -100,6 +100,10 @@ void SetWindowTitle(const char *title);
 
 /// Take a screenshot using libtiff, libpng or sdl2
 int Screenshot(const char *fname, bool convert = false);
+#ifdef GLVIS_USE_LIBPNG
+int SaveAsPNG(const char *fname, int w, int h, bool is_hidpi,
+              bool with_alpha=false);
+#endif
 
 /// Send a sequence of keystrokes to the visualization window
 void SendKeySequence(const char *seq);

makefile

@@ -92,13 +92,13 @@ GLVIS_LDFLAGS ?=
 # emcc is used when building the wasm/js version
 EMCC      ?= emcc -std=c++11
 FONT_FILE ?= OpenSans.ttf
-EMCC_OPTS ?= -s USE_SDL=2 -s USE_FREETYPE=1
+EMCC_OPTS ?= -s USE_SDL=2 -s USE_FREETYPE=1 -s USE_LIBPNG=1
 # TODO: we don't want to have DISABLE_DEPRECATED_FIND_EVENT_TARGET_BEHAVIOR=0
 # longterm but until the SDL layer supports non-default canvas ids we need this
 EMCC_LIBS ?= -s USE_SDL=2 --bind -s ALLOW_MEMORY_GROWTH=1 -s SINGLE_FILE=1 \
  --no-heap-copy -s ENVIRONMENT=web -s MODULARIZE=1 -s EXPORT_NAME=glvis \
  -s GL_ASSERTIONS=1 -s GL_DEBUG=1 -s USE_FREETYPE=1 -s MAX_WEBGL_VERSION=2 \
- -s DISABLE_DEPRECATED_FIND_EVENT_TARGET_BEHAVIOR=0
+ -s DISABLE_DEPRECATED_FIND_EVENT_TARGET_BEHAVIOR=0 --minify 0
 
 # Flags used when $(GLVIS_DEBUG) is not the same as $(MFEM_DEBUG)
 CXX11FLAG ?= -std=c++11
@@ -266,7 +266,7 @@ BYTECODE_FILES       = $(WEB_SOURCE_FILES:.cpp=.bc)
 	$(CCC) -o $@ -c $<
 
 %.bc: %.cpp
-	$(EMCC) $(EMCC_OPTS) -c $< -o $@
+	$(EMCC) $(EMCC_OPTS) $(GLVIS_FLAGS) -c $< -o $@
 
 glvis:	glvis.cpp lib/libglvis.a $(CONFIG_MK) $(MFEM_LIB_FILE)
 	$(CCC) -o glvis glvis.cpp -Llib -lglvis $(LIBS)