Added Save Screenshot

Pressing the MOD + Q key will save a screenshot the next time the screen is rendered.

It saves a PNG file with a date time stamp filename.

It uses lodepng to encode the file.  Thanks Lode Vandevenne (https://github.com/lvandeve/lodepng)

The save_screenshot function has been modified from user1902824 (https://stackoverflow.com/questions/34255820/save-sdl-texture-to-file)

Limitations.

If 2 screenshots are taken within the same second, the file name will be the same and the first file will be overwritten

Does not handle client side screen rotation.

app/meson.build

@@ -20,6 +20,7 @@ src = [
     'src/stream.c',
     'src/tiny_xpm.c',
     'src/video_buffer.c',
+    'src/lodepng.c',
     'src/util/net.c',
     'src/util/process.c',
     'src/util/str_util.c'

app/src/input_manager.c

@@ -456,6 +456,11 @@ input_manager_process_key(struct input_manager *im,
                     screen_switch_fullscreen(im->screen);
                 }
                 return;
+            case SDLK_q:
+                if (!shift && !repeat && down) {
+                   im->screen->save_screenshot = true;
+                }
+                return;
             case SDLK_w:
                 if (!shift && !repeat && down) {
                     screen_resize_to_fit(im->screen);

app/src/screen.c

@@ -2,6 +2,7 @@
 
 #include <assert.h>
 #include <string.h>
+#include <time.h>
 #include <SDL2/SDL.h>
 
 #include "config.h"
@@ -11,6 +12,7 @@
 #include "scrcpy.h"
 #include "tiny_xpm.h"
 #include "video_buffer.h"
+#include "lodepng.h"
 #include "util/lock.h"
 #include "util/log.h"
 
@@ -471,12 +473,107 @@ screen_update_frame(struct screen *screen, struct video_buffer *vb) {
     return true;
 }
 
+
+void
+save_screenshot(struct screen *screen) {
+    char filename[40];
+    struct tm *timenow;
+    SDL_Texture *ren_tex;
+    SDL_Surface *surf;
+    int st;
+    int w;
+    int h;
+    int format;
+    void *pixels;
+
+    pixels  = NULL;
+    surf    = NULL;
+    ren_tex = NULL;
+    format  = SDL_PIXELFORMAT_RGBA32;
+
+    //Create filename
+    time_t now = time(NULL);
+    timenow = localtime(&now);
+    strftime(filename, sizeof(filename), "screenshot_%Y%m%d%H%M%S.png", timenow);
+
+    // Get information about texture we want to save
+    st = SDL_QueryTexture(screen->texture, NULL, NULL, &w, &h);
+    if (st != 0) {
+        LOGE("Failed querying texture: %s\n", SDL_GetError());
+        goto cleanup;
+    }
+
+    ren_tex = SDL_CreateTexture(screen->renderer, format, SDL_TEXTUREACCESS_TARGET, w, h);
+    if (!ren_tex) {
+        LOGE("Failed creating render texture: %s\n", SDL_GetError());
+        goto cleanup;
+    }
+
+    // Initialize our canvas, then copy texture to a target whose pixel data we
+    // can access
+
+    st = SDL_SetRenderTarget(screen->renderer, ren_tex);
+    if (st != 0) {
+        LOGE("Failed setting render target: %s\n", SDL_GetError());
+        goto cleanup;
+    }
+
+    SDL_SetRenderDrawColor(screen->renderer, 0x00, 0x00, 0x00, 0x00);
+    SDL_RenderClear(screen->renderer);
+
+    st = SDL_RenderCopy(screen->renderer, screen->texture, NULL, NULL);
+    if (st != 0) {
+        LOGE("Failed copying texture data: %s\n", SDL_GetError());
+        goto cleanup;
+    }
+
+    // Create buffer to hold texture data and load it
+    pixels = malloc(w * h * SDL_BYTESPERPIXEL(format));
+    if (!pixels) {
+        LOGE("Failed allocating memory\n");
+        goto cleanup;
+    }
+
+    st = SDL_RenderReadPixels(screen->renderer, NULL, format, pixels, w * SDL_BYTESPERPIXEL(format));
+    if (st != 0) {
+        LOGE("Failed reading pixel data: %s\n", SDL_GetError());
+        goto cleanup;
+    }
+
+    // Copy pixel data over to surface
+    surf = SDL_CreateRGBSurfaceWithFormatFrom(pixels, w, h, SDL_BITSPERPIXEL(format), w * SDL_BYTESPERPIXEL(format), format);
+    if (!surf) {
+        LOGE("Failed creating new surface: %s\n", SDL_GetError());
+        goto cleanup;
+    }
+
+    // Save result to an image
+    st = lodepng_encode_file(filename, surf->pixels, w, h, LCT_RGBA, 8);
+    if (st != 0) {
+        LOGE("Failed saving image: %s\n", SDL_GetError());
+        goto cleanup;
+    }
+
+    LOGI("Saved screenshot to \"%s\"\n", filename);
+
+cleanup:
+    SDL_FreeSurface(surf);
+    free(pixels);
+    SDL_DestroyTexture(ren_tex);
+}
+
+
 void
 screen_render(struct screen *screen, bool update_content_rect) {
     if (update_content_rect) {
         screen_update_content_rect(screen);
     }
 
+    if (screen->save_screenshot) {
+        screen->save_screenshot = false;
+        save_screenshot(screen);
+    }
+
     SDL_RenderClear(screen->renderer);
     if (screen->rotation == 0) {
         SDL_RenderCopy(screen->renderer, screen->texture, NULL, &screen->rect);

app/src/screen.h

@@ -34,6 +34,7 @@ struct screen {
     bool maximized;
     bool no_window;
     bool mipmaps;
+    bool save_screenshot;
 };
 
 #define SCREEN_INITIALIZER { \
@@ -67,6 +68,7 @@ struct screen {
     .maximized = false, \
     .no_window = false, \
     .mipmaps = false, \
+    .save_screenshot = false,\
 }
 
 // initialize default values