Added parameter to take screenshot with screendump as PNG

Currently screendump only supports PPM format, which is un-compressed. Added
a "format" parameter to QMP and HMP screendump command to support PNG image
capture using libpng.

QMP example usage:
{ "execute": "screendump", "arguments": { "filename": "/tmp/image",
"format":"png" } }

HMP example usage:
screendump /tmp/image -f png

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/718

Signed-off-by: Kshitij Suri <kshitij.suri@nutanix.com>

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20220408071336.99839-3-kshitij.suri@nutanix.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hmp-commands.hx

@@ -244,10 +244,11 @@ ERST
 
     {
         .name       = "screendump",
-        .args_type  = "filename:F,device:s?,head:i?",
-        .params     = "filename [device [head]]",
+        .args_type  = "filename:F,format:-fs,device:s?,head:i?",
+        .params     = "filename [-f format] [device [head]]",
         .help       = "save screen from head 'head' of display device 'device'"
-                      "into PPM image 'filename'",
+                      "in specified format 'format' as image 'filename'."
+                      "Currently only 'png' and 'ppm' formats are supported.",
          .cmd        = hmp_screendump,
         .coroutine  = true,
     },

monitor/hmp-cmds.c

@@ -1720,9 +1720,19 @@ hmp_screendump(Monitor *mon, const QDict *qdict)
     const char *filename = qdict_get_str(qdict, "filename");
     const char *id = qdict_get_try_str(qdict, "device");
     int64_t head = qdict_get_try_int(qdict, "head", 0);
+    const char *input_format  = qdict_get_try_str(qdict, "format");
     Error *err = NULL;
+    ImageFormat format;
 
-    qmp_screendump(filename, id != NULL, id, id != NULL, head, &err);
+    format = qapi_enum_parse(&ImageFormat_lookup, input_format,
+                              IMAGE_FORMAT_PPM, &err);
+    if (err) {
+        goto end;
+    }
+
+    qmp_screendump(filename, id != NULL, id, id != NULL, head,
+                   input_format != NULL, format, &err);
+end:
     hmp_handle_error(mon, err);
 }
 

qapi/ui.json

@@ -157,12 +157,27 @@
 ##
 { 'command': 'expire_password', 'boxed': true, 'data': 'ExpirePasswordOptions' }
 
+##
+# @ImageFormat:
+#
+# Supported image format types.
+#
+# @png: PNG format
+#
+# @ppm: PPM format
+#
+# Since: 7.1
+#
+##
+{ 'enum': 'ImageFormat',
+  'data': ['ppm', 'png'] }
+
 ##
 # @screendump:
 #
-# Write a PPM of the VGA screen to a file.
+# Capture the contents of a screen and write it to a file.
 #
-# @filename: the path of a new PPM file to store the image
+# @filename: the path of a new file to store the image
 #
 # @device: ID of the display device that should be dumped. If this parameter
 #          is missing, the primary display will be used. (Since 2.12)
@@ -171,6 +186,8 @@
 #        parameter is missing, head #0 will be used. Also note that the head
 #        can only be specified in conjunction with the device ID. (Since 2.12)
 #
+# @format: image format for screendump. (default: ppm) (Since 7.1)
+#
 # Returns: Nothing on success
 #
 # Since: 0.14
@@ -183,7 +200,8 @@
 #
 ##
 { 'command': 'screendump',
-  'data': {'filename': 'str', '*device': 'str', '*head': 'int'},
+  'data': {'filename': 'str', '*device': 'str', '*head': 'int',
+           '*format': 'ImageFormat'},
   'coroutine': true }
 
 ##

ui/console.c

@@ -37,6 +37,9 @@
 #include "exec/memory.h"
 #include "io/channel-file.h"
 #include "qom/object.h"
+#ifdef CONFIG_PNG
+#include <png.h>
+#endif
 
 #define DEFAULT_BACKSCROLL 512
 #define CONSOLE_CURSOR_PERIOD 500
@@ -291,6 +294,89 @@ void graphic_hw_invalidate(QemuConsole *con)
     }
 }
 
+#ifdef CONFIG_PNG
+/**
+ * png_save: Take a screenshot as PNG
+ *
+ * Saves screendump as a PNG file
+ *
+ * Returns true for success or false for error.
+ *
+ * @fd: File descriptor for PNG file.
+ * @image: Image data in pixman format.
+ * @errp: Pointer to an error.
+ */
+static bool png_save(int fd, pixman_image_t *image, Error **errp)
+{
+    int width = pixman_image_get_width(image);
+    int height = pixman_image_get_height(image);
+    g_autofree png_struct *png_ptr = NULL;
+    g_autofree png_info *info_ptr = NULL;
+    g_autoptr(pixman_image_t) linebuf =
+                            qemu_pixman_linebuf_create(PIXMAN_a8r8g8b8, width);
+    uint8_t *buf = (uint8_t *)pixman_image_get_data(linebuf);
+    FILE *f = fdopen(fd, "wb");
+    int y;
+    if (!f) {
+        error_setg_errno(errp, errno,
+                         "Failed to create file from file descriptor");
+        return false;
+    }
+
+    png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL,
+                                      NULL, NULL);
+    if (!png_ptr) {
+        error_setg(errp, "PNG creation failed. Unable to write struct");
+        fclose(f);
+        return false;
+    }
+
+    info_ptr = png_create_info_struct(png_ptr);
+
+    if (!info_ptr) {
+        error_setg(errp, "PNG creation failed. Unable to write info");
+        fclose(f);
+        png_destroy_write_struct(&png_ptr, &info_ptr);
+        return false;
+    }
+
+    png_init_io(png_ptr, f);
+
+    png_set_IHDR(png_ptr, info_ptr, width, height, 8,
+                 PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE,
+                 PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
+
+    png_write_info(png_ptr, info_ptr);
+
+    for (y = 0; y < height; ++y) {
+        qemu_pixman_linebuf_fill(linebuf, image, width, 0, y);
+        png_write_row(png_ptr, buf);
+    }
+    qemu_pixman_image_unref(linebuf);
+
+    png_write_end(png_ptr, NULL);
+
+    png_destroy_write_struct(&png_ptr, &info_ptr);
+
+    if (fclose(f) != 0) {
+        error_setg_errno(errp, errno,
+                         "PNG creation failed. Unable to close file");
+        return false;
+    }
+
+    return true;
+}
+
+#else /* no png support */
+
+static bool png_save(int fd, pixman_image_t *image, Error **errp)
+{
+    error_setg(errp, "Enable PNG support with libpng for screendump");
+    return false;
+}
+
+#endif /* CONFIG_PNG */
+
 static bool ppm_save(int fd, pixman_image_t *image, Error **errp)
 {
     int width = pixman_image_get_width(image);
@@ -329,7 +415,8 @@ static void graphic_hw_update_bh(void *con)
 /* Safety: coroutine-only, concurrent-coroutine safe, main thread only */
 void coroutine_fn
 qmp_screendump(const char *filename, bool has_device, const char *device,
-               bool has_head, int64_t head, Error **errp)
+               bool has_head, int64_t head,
+               bool has_format, ImageFormat format, Error **errp)
 {
     g_autoptr(pixman_image_t) image = NULL;
     QemuConsole *con;
@@ -385,10 +472,18 @@ qmp_screendump(const char *filename, bool has_device, const char *device,
      * yields and releases the BQL. It could produce corrupted dump, but
      * it should be otherwise safe.
      */
+    if (has_format && format == IMAGE_FORMAT_PNG) {
+        /* PNG format specified for screendump */
+        if (!png_save(fd, image, errp)) {
+            qemu_unlink(filename);
+        }
+    } else {
+        /* PPM format specified/default for screendump */
         if (!ppm_save(fd, image, errp)) {
             qemu_unlink(filename);
         }
     }
+}
 
 void graphic_hw_text_update(QemuConsole *con, console_ch_t *chardata)
 {