swap RGB -> BGR when necessary

src/main.c

@@ -824,6 +824,7 @@ static void canvas_render(GtkGLArea *area, GdkGLContext *context, gpointer data)
           render->preview = true;
           render->updated_at = tick;
           render->y_invert = frame->y_invert;
+          render->swap_rgb = frame->swap_rgb;
         }
       } else if (render->preview
           || render->pixels == NULL || size_changed(render)) {
@@ -839,6 +840,7 @@ static void canvas_render(GtkGLArea *area, GdkGLContext *context, gpointer data)
         render->tex_stride = cairo_image_surface_get_stride(head->surface);
         render->updated_at = tick;
         render->y_invert = false;
+        render->swap_rgb = false;
       }
     }
   }

src/outputs.c

@@ -174,8 +174,13 @@ static void capture_buffer(void *data,
     struct zwlr_screencopy_frame_v1 *copy_frame,
     uint32_t format, uint32_t width, uint32_t height, uint32_t stride) {
   struct wd_frame *frame = data;
-
   char *shm_name = NULL;
+
+  if (format != WL_SHM_FORMAT_ARGB8888 && format != WL_SHM_FORMAT_XRGB8888 &&
+      format != WL_SHM_FORMAT_ABGR8888 && format != WL_SHM_FORMAT_XBGR8888) {
+    goto err;
+  }
+
   if (asprintf(&shm_name, "/wd-%s", frame->output->name) == -1) {
     fprintf(stderr, "asprintf: %s\n", strerror(errno));
     shm_name = NULL;
@@ -199,6 +204,8 @@ static void capture_buffer(void *data,
   frame->stride = stride;
   frame->width = width;
   frame->height = height;
+  frame->swap_rgb = format == WL_SHM_FORMAT_ABGR8888
+    || format == WL_SHM_FORMAT_XBGR8888;
 
   return;
 err:

src/render.c

@@ -53,6 +53,7 @@ struct wd_gl_data {
   GLuint texture_uv_attribute;
   GLuint texture_screen_size_uniform;
   GLuint texture_texture_uniform;
+  GLuint texture_color_transform_uniform;
 
   GLuint buffers[2];
 
@@ -93,8 +94,9 @@ void main(void) {\n\
 static const char *texture_fragment_shader_src = "\
 varying vec2 uv_out;\n\
 uniform sampler2D texture;\n\
+uniform mat4 color_transform;\n\
 void main(void) {\n\
-  gl_FragColor = texture2D(texture, uv_out);\n\
+  gl_FragColor = texture2D(texture, uv_out) * color_transform;\n\
 }";
 
 static GLuint gl_make_shader(GLenum type, const char *src) {
@@ -182,6 +184,8 @@ struct wd_gl_data *wd_gl_setup(void) {
       "screen_size");
   res->texture_texture_uniform = glGetUniformLocation(res->texture_program,
       "texture");
+  res->texture_color_transform_uniform = glGetUniformLocation(
+      res->texture_program, "color_transform");
 
   glGenBuffers(2, res->buffers);
   glBindBuffer(GL_ARRAY_BUFFER, res->buffers[0]);
@@ -195,6 +199,18 @@ struct wd_gl_data *wd_gl_setup(void) {
   return res;
 }
 
+static const GLfloat TRANSFORM_RGB[16] = {
+  1, 0, 0, 0,
+  0, 1, 0, 0,
+  0, 0, 1, 0,
+  0, 0, 0, 1};
+
+static const GLfloat TRANSFORM_BGR[16] = {
+  0, 0, 1, 0,
+  0, 1, 0, 0,
+  1, 0, 0, 0,
+  0, 0, 0, 1};
+
 #define PUSH_POINT(_start, _a, _b) \
     *((_start)++) = (_a);\
     *((_start)++) = (_b);
@@ -278,6 +294,8 @@ void wd_gl_render(struct wd_gl_data *res, struct wd_render_data *info,
             0, GL_RGBA, GL_UNSIGNED_BYTE, head->pixels);
         glPixelStorei(GL_UNPACK_ROW_LENGTH_EXT, 0);
       }
+      glUniformMatrix4fv(res->texture_color_transform_uniform, 1, GL_FALSE,
+        head->swap_rgb ? TRANSFORM_RGB : TRANSFORM_BGR);
       glDrawArrays(GL_TRIANGLES, i * 6, 6);
     }
   }

src/wdisplays.h

@@ -90,6 +90,7 @@ struct wd_frame {
   uint8_t *pixels;
   uint64_t tick;
   bool y_invert;
+  bool swap_rgb;
 };
 
 struct wd_head_config {
@@ -154,6 +155,7 @@ struct wd_render_head_data {
   unsigned tex_height;
   bool preview;
   bool y_invert;
+  bool swap_rgb;
   uint64_t updated_at;
 
   bool hovered;