src/utils_glx.c: Avoid RGBA to BGRA conversion in software.

Speed up bitmap loading by avoiding conversions in software. The
GPU stores a bitmap internally in BGRA format instead of RGBA. By
using BGRA iso RGBA for format to load this conversion is ommitted
and a considerable speedup is obtained.

src/utils_glx.c

@@ -796,7 +796,8 @@ gl_destroy_texture(
         abort();
 
     glEnable(target);
-    glDeleteTextures(1, texture);
+    if (glIsTexture(*texture))
+        glDeleteTextures(1, texture);
     glDisable(target);
 }
 
@@ -855,6 +856,12 @@ gl_create_texture(
         break;
     case GL_RGBA:
     case GL_BGRA:
+        /* NOTE: the GPU expects pixel data in BGRA format,
+         * otherwise it will do a conversion in software
+         * which is of course much slower then just copying
+         * the data into the GPU.
+         */
+        format = GL_BGRA;
         internal_format = GL_RGBA;
         bytes_per_component = 4;
         break;
@@ -874,10 +881,13 @@ gl_create_texture(
 
     glEnable(target);
     glGenTextures(1, &texture);
+    if (gl_check_error())
+        abort();
     glBindTexture(target, texture);
     gl_set_texture_scaling(target, GL_LINEAR);
     gl_set_texture_wrapping(target, GL_CLAMP_TO_EDGE);
     glPixelStorei(GL_UNPACK_ALIGNMENT, bytes_per_component);
+    //glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
     switch (target) {
     case GL_TEXTURE_1D:
         glTexImage1D(
@@ -1209,6 +1219,7 @@ gl_destroy_shader_object(GLShaderObject *so)
 
     gl_unbind_shader_object(so);
 
+
     if (so->shader) {
         gl_vtable->gl_delete_programs(1, &so->shader);
         so->shader = 0;