Evas gl_x11: Add support for glReadPixels

This will be needed by the filters for proxy rendering,
for textures and maps (displacement).

Add new engine functions to unleash the (sluggish) power of glReadPixels.
The idea is to be able to bypass glReadPixels later, so 3 new APIs are
added:
- surface_lock
- surface_read_pixels
- surface_unlock
They must be called in that order.

Note (for history):
glReadPixels was always getting the wrong data during first draw,
but the right data during a redraw...
Why? Well simply because for OpenGL itself, the image had never
been drawn in teh first place! Only the Evas GL context knew
about the image drawing, as it was queued somewhere in the pipe.

One line solution: Call evas_gl_common_context_flush before
doing anything else.

src/lib/evas/include/evas_private.h

@@ -907,8 +907,11 @@ struct _Evas_Func
    void *(*gl_proc_address_get)          (void *data, const char *name);
    int  (*gl_native_surface_get)         (void *data, void *surface, void *native_surface);
    void *(*gl_api_get)                   (void *data);
-   void (*gl_direct_override_get)       (void *data, int *override, int *force_off);
+   void (*gl_direct_override_get)        (void *data, int *override, int *force_off);
    void (*gl_get_pixels_set)             (void *data, void *get_pixels, void *get_pixels_data, void *obj);
+   Eina_Bool (*gl_surface_lock)          (void *data, void *surface);
+   Eina_Bool (*gl_surface_read_pixels)   (void *data, void *surface, int x, int y, int w, int h, Evas_Colorspace cspace, void *pixels);
+   Eina_Bool (*gl_surface_unlock)        (void *data, void *surface);
 
    int  (*image_load_error_get)          (void *data, void *image);
    int  (*font_run_end_get)              (void *data, Evas_Font_Set *font, Evas_Font_Instance **script_fi, Evas_Font_Instance **cur_fi, Evas_Script_Type script, const Eina_Unicode *text, int run_len);

src/modules/evas/engines/gl_common/evas_gl_common.h

@@ -628,6 +628,7 @@ struct _Evas_GL_Image
    unsigned char    cached : 1;
    unsigned char    alpha : 1;
    unsigned char    tex_only : 1;
+   unsigned char    locked : 1; // gl_surface_lock/unlock
 };
 
 struct _Evas_GL_Font_Texture
@@ -838,6 +839,8 @@ extern void       (*glsym_glReleaseShaderCompiler)(void);
 extern void      *(*glsym_glMapBuffer)            (GLenum a, GLenum b);
 extern GLboolean  (*glsym_glUnmapBuffer)          (GLenum a);
 
+extern void       (*glsym_glReadPixels)           (GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, GLvoid *data);
+
 #ifdef GL_GLES
 extern void          *(*secsym_eglCreateImage)               (void *a, void *b, GLenum c, void *d, const int *e);
 extern unsigned int   (*secsym_eglDestroyImage)              (void *a, void *b);

src/modules/evas/engines/gl_common/evas_gl_context.c

@@ -29,6 +29,7 @@ void      *(*glsym_glMapBuffer)            (GLenum a, GLenum b) = NULL;
 GLboolean  (*glsym_glUnmapBuffer)          (GLenum a) = NULL;
 void       (*glsym_glStartTiling)          (GLuint a, GLuint b, GLuint c, GLuint d, GLuint e) = NULL;
 void       (*glsym_glEndTiling)            (GLuint a) = NULL;
+void       (*glsym_glReadPixels)           (GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, GLvoid *data) = NULL;
 
 #ifdef GL_GLES
 // just used for finding symbols :)
@@ -211,6 +212,8 @@ gl_symbols(void)
 
    FINDSYM(secsym_eglGetImageAttribSEC, "eglGetImageAttribSEC", secsym_func_uint);
 #endif
+
+   FINDSYM(glsym_glReadPixels, "glReadPixels", glsym_func_void);
 }
 
 static void shader_array_flush(Evas_Engine_GL_Context *gc);

src/modules/evas/engines/gl_x11/evas_engine.c

@@ -3371,6 +3371,65 @@ eng_gl_get_pixels_set(void *data, void *get_pixels, void *get_pixels_data, void
    re->func.get_pixels_data = get_pixels_data;
    re->func.obj = (Evas_Object*)obj;
 }
+
+static Eina_Bool
+eng_gl_surface_lock(void *data, void *surface)
+{
+   Render_Engine *re = data;
+   Evas_GL_Image *im = surface;
+
+   EVGLINIT(re, EINA_FALSE);
+   if (!im->tex || !im->tex->pt)
+     {
+        ERR("Can not lock image that is not a surface!");
+        return EINA_FALSE;
+     }
+
+   evas_gl_common_context_flush(im->gc);
+   im->locked = EINA_TRUE;
+   return EINA_TRUE;
+}
+
+static Eina_Bool
+eng_gl_surface_unlock(void *data, void *surface)
+{
+   Render_Engine *re = data;
+   Evas_GL_Image *im = surface;
+
+   EVGLINIT(re, EINA_FALSE);
+   im->locked = EINA_FALSE;
+   return EINA_TRUE;
+}
+
+static Eina_Bool
+eng_gl_surface_read_pixels(void *data, void *surface,
+                           int x, int y, int w, int h,
+                           Evas_Colorspace cspace, void *pixels)
+{
+   Render_Engine *re = data;
+   Evas_GL_Image *im = surface;
+
+   EINA_SAFETY_ON_NULL_RETURN_VAL(pixels, EINA_FALSE);
+
+   EVGLINIT(re, EINA_FALSE);
+   if (!im->locked)
+     {
+        // For now, this is useless, but let's force clients to lock :)
+        CRI("The surface must be locked before reading its pixels!");
+        return EINA_FALSE;
+     }
+
+   if (cspace != EVAS_COLORSPACE_ARGB8888)
+     {
+        ERR("Conversion to colorspace %d is not supported!", (int) cspace);
+        return EINA_FALSE;
+     }
+
+   glsym_glBindFramebuffer(GL_READ_FRAMEBUFFER, im->tex->pt->fb);
+   glsym_glReadPixels(x, y, w, h, GL_BGRA, GL_UNSIGNED_BYTE, pixels);
+   glsym_glBindFramebuffer(GL_READ_FRAMEBUFFER, 0);
+   return EINA_TRUE;
+}
 //--------------------------------//
 
 static int
@@ -3696,6 +3755,9 @@ module_open(Evas_Module *em)
    ORD(gl_api_get);
    ORD(gl_direct_override_get);
    ORD(gl_get_pixels_set);
+   ORD(gl_surface_lock);
+   ORD(gl_surface_read_pixels);
+   ORD(gl_surface_unlock);
 
    ORD(image_load_error_get);
 

src/modules/evas/engines/software_generic/evas_engine.c

@@ -2692,6 +2692,9 @@ static Evas_Func func =
      NULL, // need software mesa for gl rendering <- gl_api_get
      NULL, // need software mesa for gl rendering <- gl_direct_override
      NULL, // need software mesa for gl rendering <- gl_get_pixels_set
+     NULL, // need software mesa for gl rendering <- gl_surface_lock
+     NULL, // need software mesa for gl rendering <- gl_surface_read_pixels
+     NULL, // need software mesa for gl rendering <- gl_surface_unlock
      eng_image_load_error_get,
      eng_font_run_font_end_get,
      eng_image_animated_get,