Historically, QEMU took screenshots in PPM. While this might use
to be popular format, as of v7.1.0-rc0~125^2~6 it is possible to
take screenshots in PNG. This is more popular and renders almost
everywhere, which is not the case for PPM (for instance, modern
browsers do not render it).

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
---
 src/qemu/qemu_driver.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index f6683cbb0a..d509582719 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -3291,6 +3291,7 @@ qemuDomainScreenshot(virDomainPtr dom,
     const char *videoAlias = NULL;
     char *ret = NULL;
     bool unlink_tmp = false;
+    const char *format = NULL;
 
     virCheckFlags(0, NULL);
 
@@ -3339,6 +3340,10 @@ qemuDomainScreenshot(virDomainPtr dom,
         }
     }
 
+    if (virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_SCREENSHOT_FORMAT_PNG)) {
+        format = "png";
+    }
+
     tmp = g_strdup_printf("%s/qemu.screendump.XXXXXX", priv->libDir);
 
     if ((tmp_fd = g_mkstemp_full(tmp, O_RDWR | O_CLOEXEC, S_IRUSR | S_IWUSR)) == -1) {
@@ -3350,7 +3355,7 @@ qemuDomainScreenshot(virDomainPtr dom,
     qemuSecurityDomainSetPathLabel(driver, vm, tmp, false);
 
     qemuDomainObjEnterMonitor(vm);
-    if (qemuMonitorScreendump(priv->mon, videoAlias, screen, NULL, tmp) < 0) {
+    if (qemuMonitorScreendump(priv->mon, videoAlias, screen, format, tmp) < 0) {
         qemuDomainObjExitMonitor(vm);
         goto endjob;
     }
@@ -3367,7 +3372,11 @@ qemuDomainScreenshot(virDomainPtr dom,
         goto endjob;
     }
 
-    ret = g_strdup("image/x-portable-pixmap");
+    if (STREQ_NULLABLE(format, "png")) {
+        ret = g_strdup("image/png");
+    } else {
+        ret = g_strdup("image/x-portable-pixmap");
+    }
 
  endjob:
     VIR_FORCE_CLOSE(tmp_fd);
-- 
2.37.4

On Wed, Dec 07, 2022 at 12:20:52PM +0100, Michal Privoznik wrote:
>Historically, QEMU took screenshots in PPM. While this might use
>to be popular format, as of v7.1.0-rc0~125^2~6 it is possible to
>take screenshots in PNG. This is more popular and renders almost
>everywhere, which is not the case for PPM (for instance, modern
>browsers do not render it).
>
>Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
>---
> src/qemu/qemu_driver.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
>diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
>index f6683cbb0a..d509582719 100644
>--- a/src/qemu/qemu_driver.c
>+++ b/src/qemu/qemu_driver.c
>@@ -3291,6 +3291,7 @@ qemuDomainScreenshot(virDomainPtr dom,
>     const char *videoAlias = NULL;
>     char *ret = NULL;
>     bool unlink_tmp = false;
>+    const char *format = NULL;
>
>     virCheckFlags(0, NULL);
>
>@@ -3339,6 +3340,10 @@ qemuDomainScreenshot(virDomainPtr dom,
>         }
>     }
>
>+    if (virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_SCREENSHOT_FORMAT_PNG)) {
>+        format = "png";
>+    }
>+

Curly brackets are discouraged for one-line condition bodies IIRC ;)