Images in X11 backend only works with RGBA

[TomJGooding]

For example, nk_xsurf_load_image_from_file("lena.png") will display a garbled RGB image and segfault if you try to resize the window.

$ file lena.png 
lena.png: PNG image data, 512 x 512, 8-bit/color RGB, non-interlaced

/* --snip-- */
#define NK_IMPLEMENTATION
#define NK_XLIB_IMPLEMENTATION
#define NK_XLIB_INCLUDE_STB_IMAGE
#define NK_XLIB_IMPLEMENT_STB_IMAGE
#include "../../nuklear.h"
#include "nuklear_xlib.h"

/* --snip-- */
    struct nk_image img = nk_xsurf_load_image_from_file("lena.png");

    while (running)
    {
        /* --snip-- */
        if (nk_begin(ctx, "Image", nk_rect(0, 0, 300, 300), NK_WINDOW_SCALABLE))
        {
            float win_h = nk_window_get_content_region(ctx).h;
            nk_layout_row_dynamic(ctx, win_h, 1);
            nk_image(ctx, img);
        }
        nk_end(ctx);
        /* --snip-- */

[TomJGooding]

I realise the images in other demos are all RGBA so I wasn't sure about creating an issue for this. But the code seems to suggest this was intended to support other image formats?

Nuklear/demo/x11/nuklear_xlib.h

Lines 502 to 503 in a4e125f

	/* rgba to bgra */
	if (channels >= 3){

I'm still new to all this, but my quick solution was to set the desired_channels to 4 in the call to stbi_load:

diff --git a/demo/x11/nuklear_xlib.h b/demo/x11/nuklear_xlib.h
index 1605bf4..608ad98 100644
--- a/demo/x11/nuklear_xlib.h
+++ b/demo/x11/nuklear_xlib.h
@@ -556,7 +556,7 @@ nk_xsurf_load_image_from_file(char const *filename)
 {
     int x,y,n;
     unsigned char *data;
-    data = stbi_load(filename, &x, &y, &n, 0);
+    data = stbi_load(filename, &x, &y, &n, 4);
     return nk_stbi_image_to_xsurf(data, x, y, n);
 }
 #endif /* NK_XLIB_INCLUDE_STB_IMAGE */

[RobLoach]

Thanks! Would you be willing to send a Pull Request for this change?

[TomJGooding]

Sorry I should have clarified, but simply changing the stbi_load channels was really just my quick workaround rather than a suggested fix! Like I say I'm still very new to all this, so I was hoping someone with better knowledge of XCreateImage etc. might have better ideas!

[sleeptightAnsiC]

Followup from #952 (comment)

The whole problem here is that desired blp is not equal to actual image channels in nk_stbi_image_to_xsurf, which in this case ends up reading/writing pass data's end.

I was able to repro this with the file and diff from below:

lena.zip

diff

diff --git a/demo/x11/Makefile b/demo/x11/Makefile
index edd4658..aec373a 100644
--- a/demo/x11/Makefile
+++ b/demo/x11/Makefile
@@ -2,7 +2,8 @@
 BIN = demo
 
 # Flags
-CFLAGS += -g -std=c89 -Wall -Wextra -pedantic -Wno-unused-function -D_POSIX_C_SOURCE=200809L
+#CFLAGS += -g -std=c89 -Wall -Wextra -pedantic -Wno-unused-function -D_POSIX_C_SOURCE=200809L
+CFLAGS += -g -Wall -Wextra -D_POSIX_C_SOURCE=200809L -Wno-unused-function -Wno-misleading-indentation -Wno-shift-negative-value -fsanitize=address -fstack-protector
 
 SRC = main.c
 OBJ = $(SRC:.c=.o)
diff --git a/demo/x11/main.c b/demo/x11/main.c
index e5d6900..1b0c3bc 100644
--- a/demo/x11/main.c
+++ b/demo/x11/main.c
@@ -15,6 +15,8 @@
 #define NK_INCLUDE_STANDARD_VARARGS
 #define NK_INCLUDE_DEFAULT_ALLOCATOR
 #define NK_IMPLEMENTATION
+#define NK_XLIB_INCLUDE_STB_IMAGE
+#define NK_XLIB_IMPLEMENT_STB_IMAGE
 #define NK_XLIB_IMPLEMENTATION
 #include "../../nuklear.h"
 #include "nuklear_xlib.h"
@@ -125,6 +127,7 @@ main(void)
     int running = 1;
     XWindow xw;
     struct nk_context *ctx;
+    struct nk_image img;
 
     #ifdef INCLUDE_CONFIGURATOR
     static struct nk_color color_table[NK_COLOR_COUNT];
@@ -168,6 +171,8 @@ main(void)
     ctx = nk_xlib_init(xw.font, xw.dpy, xw.screen, xw.win, xw.width, xw.height);
 #endif
 
+    img = nk_xsurf_load_image_from_file("bin/lena.png");
+
     while (running)
     {
         /* Input */
@@ -203,6 +208,14 @@ main(void)
         nk_end(ctx);
         if (nk_window_is_hidden(ctx, "Demo")) break;
 
+        if (nk_begin(ctx, "Image", nk_rect(0, 0, 300, 300), NK_WINDOW_SCALABLE))
+        {
+            float win_h = nk_window_get_content_region(ctx).h;
+            nk_layout_row_dynamic(ctx, win_h, 1);
+            nk_image(ctx, img);
+        }
+        nk_end(ctx);
+
         /* -------------- EXAMPLES ---------------- */
         #ifdef INCLUDE_CALCULATOR
           calculator(ctx);

I think, the correct way to fix it, is doing stbi_load after getting bpl, not before it.

EDIT: submitted PR at #954