implement OpenGL screenshot

src/drawing/engines/opengl/OpenGLDrawingEngine.cpp

@@ -47,6 +47,7 @@ IDrawingEngine * DrawingEngineFactory::CreateOpenGL()
 extern "C"
 {
     #include "../../../config.h"
+    #include "../../../interface/screenshot.h"
     #include "../../../interface/window.h"
     #include "../../../intro.h"
     #include "../../drawing.h"
@@ -328,8 +329,11 @@ public:
     
     sint32 Screenshot() override
     {
-        // Not implemented
-        return -1;
+        _canvasFramebuffer->Bind();
+        void * pixels = _canvasFramebuffer->GetPixels();
+        int result = screenshot_dump_png_32bpp(_width, _height, pixels);
+        Memory::Free(pixels);
+        return result;
     }
 
     void CopyRect(sint32 x, sint32 y, sint32 width, sint32 height, sint32 dx, sint32 dy) override

src/drawing/engines/opengl/OpenGLFramebuffer.cpp

@@ -15,6 +15,7 @@
 #pragma endregion
 
 #include <SDL_video.h>
+#include "../../../core/Memory.hpp"
 #include "OpenGLFramebuffer.h"
 
 constexpr GLuint BACKBUFFER_ID = 0;
@@ -56,3 +57,24 @@ void OpenGLFramebuffer::Bind()
     glBindFramebuffer(GL_FRAMEBUFFER, _id);
     glViewport(0, 0, (GLsizei)_width, (GLsizei)_height);
 }
+
+void * OpenGLFramebuffer::GetPixels() const
+{
+    void * pixels = Memory::Allocate<void>(_width * _height * 4);
+    glReadPixels(0, 0, _width, _height, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
+
+    // Flip pixels vertically
+    void * flippedPixels = Memory::Allocate<void>(_width * _height * 4);
+    size_t stride = _width * 4;
+    uint8 * src = (uint8 *)pixels + ((_height - 1) * stride);
+    uint8 * dst = (uint8 *)flippedPixels;
+    for (sint32 y = 0; y < _height; y++)
+    {
+        Memory::Copy(dst, src, stride);
+        src -= stride;
+        dst += stride;
+    }
+    Memory::Free(pixels);
+
+    return flippedPixels;
+}

src/drawing/engines/opengl/OpenGLFramebuffer.h

@@ -39,4 +39,5 @@ public:
     GLuint GetTexture() const { return _texture; }
 
     void Bind();
+    void * GetPixels() const;
 };

src/image_io.c

@@ -171,6 +171,67 @@ bool image_io_png_write(const rct_drawpixelinfo *dpi, const rct_palette *palette
 	return true;
 }
 
+static void image_io_png_warning(png_structp png_ptr, const char *b)
+{
+    log_warning(b);
+}
+
+static void image_io_png_error(png_structp png_ptr, const char *b)
+{
+    log_error(b);
+}
+
+bool image_io_png_write_32bpp(sint32 width, sint32 height, const void *pixels, const utf8 *path)
+{
+	// Setup PNG
+	png_structp png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, image_io_png_error, image_io_png_warning);
+	if (png_ptr == NULL) {
+		return false;
+	}
+
+	png_infop info_ptr = png_create_info_struct(png_ptr);
+	if (info_ptr == NULL) {
+		png_destroy_write_struct(&png_ptr, (png_infopp)NULL);
+		return false;
+	}
+
+	// Open file for writing
+	SDL_RWops *file = SDL_RWFromFile(path, "wb");
+	if (file == NULL) {
+		png_destroy_write_struct(&png_ptr, (png_infopp)NULL);
+		return false;
+	}
+	png_set_write_fn(png_ptr, file, my_png_write_data, my_png_flush);
+
+	// Set error handler
+	if (setjmp(png_jmpbuf(png_ptr))) {
+		png_destroy_write_struct(&png_ptr, &info_ptr);
+		SDL_RWclose(file);
+		return false;
+	}
+
+	// Write header
+	png_set_IHDR(
+		png_ptr, info_ptr, width, height, 8,
+		PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT
+	);
+	png_write_info(png_ptr, info_ptr);
+
+	// Write pixels
+	uint8 *bits = (uint8*)pixels;
+	for (int y = 0; y < height; y++) {
+		png_write_row(png_ptr, (png_byte *)bits);
+		bits += width * 4;
+	}
+
+	// Finish
+	png_write_end(png_ptr, NULL);
+	SDL_RWclose(file);
+
+	png_destroy_write_struct(&png_ptr, &info_ptr);
+	return true;
+}
+
 static void my_png_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
 {
 	SDL_RWops *file = (SDL_RWops*)png_get_io_ptr(png_ptr);

src/image_io.h

@@ -23,5 +23,6 @@
 bool image_io_png_read(uint8 **pixels, uint32 *width, uint32 *height, const utf8 *path);
 
 bool image_io_png_write(const rct_drawpixelinfo *dpi, const rct_palette *palette, const utf8 *path);
+bool image_io_png_write_32bpp(sint32 width, sint32 height, const void *pixels, const utf8 *path);
 
 #endif

src/interface/screenshot.c

@@ -115,6 +115,22 @@ int screenshot_dump_png(rct_drawpixelinfo *dpi)
 	}
 }
 
+int screenshot_dump_png_32bpp(sint32 width, sint32 height, const void *pixels)
+{
+	// Get a free screenshot path
+	int index;
+	char path[MAX_PATH] = "";
+	if ((index = screenshot_get_next_path(path)) == -1) {
+		return -1;
+	}
+
+	if (image_io_png_write_32bpp(width, height, pixels, path)) {
+		return index;
+	} else {
+		return -1;
+	}
+}
+
 void screenshot_giant()
 {
 	int originalRotation = get_current_rotation();

src/interface/screenshot.h

@@ -22,6 +22,7 @@
 void screenshot_check();
 int screenshot_dump();
 int screenshot_dump_png(rct_drawpixelinfo *dpi);
+int screenshot_dump_png_32bpp(sint32 width, sint32 height, const void *pixels);
 
 void screenshot_giant();
 int cmdline_for_screenshot(const char **argv, int argc);