From c4ede9fcceae854e34bc2e86d9c2a28016269f20 Mon Sep 17 00:00:00 2001
From: Allanis <allanis@saracraft.net>
Date: Wed, 15 May 2013 23:01:16 +0100
Subject: [PATCH] [Add] Check for shaders (not used yet).

---
 src/opengl.c | 34 ++++++++++++++++++++++++++++++++++
 src/opengl.h | 14 ++++++++------
 2 files changed, 42 insertions(+), 6 deletions(-)

diff --git a/src/opengl.c b/src/opengl.c
index a3d908b..9fb8fb0 100644
--- a/src/opengl.c
+++ b/src/opengl.c
@@ -38,6 +38,8 @@ static GLuint gl_loadSurface(SDL_Surface* surface, int* rw, int* rh);
 // PNG.
 int write_png(const char* file_name, png_bytep* rows, int w, int h,
               int colourtype, int bitdepth);
+// Global.
+static GLboolean gl_hasExt(char* name);
 
 // ================
 // MISC!
@@ -536,6 +538,32 @@ void gl_drawCircleInRect(const double cx, const double cy, const double r,
 // GLOBAL.
 // ================
 
+// Check for extensions.
+static GLboolean gl_hasExt(char* name) {
+  // ======================================================
+  // Search for name in the extensions string. Use of strstr()
+  // is not sufficient because extensions names can be prefixes of
+  // other extension names. Could use strtol() but the constant
+  // string returned by glGetString can be in read-only memory.
+  // ======================================================
+
+  char* p, *end;
+  size_t len, n;
+
+  p = (char*) glGetString(GL_EXTENSIONS);
+  len = strlen(name);
+  end = p + strlen(p);
+
+  while(p < end) {
+    n = strcspn(p, " ");
+    if((len == n) && (strncmp(name, p, n)==0))
+      return GL_TRUE;
+
+    p += (n+1);
+  }
+  return GL_FALSE;
+}
+
 // Initialize SDL/OpenGL etc.
 int gl_init(void) {
   int doublebuf, depth, i, j, off, toff, supported;
@@ -621,6 +649,12 @@ int gl_init(void) {
   if(doublebuf) gl_screen.flags |= OPENGL_DOUBLEBUF;
   gl_screen.depth = gl_screen.r + gl_screen.g + gl_screen.b + gl_screen.a;
 
+  // Get info about some extensions.
+  if(gl_hasExt("GL_ARB_vertex_shader")==GL_TRUE)
+    gl_screen.flags |= OPENGL_VERT_SHADER;
+  if(gl_hasExt("GL_ARB_fragment_shader")==GL_TRUE)
+    gl_screen.flags |= OPENGL_FRAG_SHADER;
+
   // Debug heaven.
   DEBUG("OpenGL Window Created: %dx%d@%dbpp %s", gl_screen.w, gl_screen.h,
         gl_screen.depth, (gl_has(OPENGL_FULLSCREEN)) ? "fullscreen" : "window");
diff --git a/src/opengl.h b/src/opengl.h
index 169a5a3..720df0f 100644
--- a/src/opengl.h
+++ b/src/opengl.h
@@ -19,12 +19,14 @@
 #define RGBMASK RMASK,GMASK,BMASK,AMASK
 
 // Info about opengl screen.
-#define OPENGL_FULLSCREEN (1<<0)
-#define OPENGL_DOUBLEBUF  (1<<1)
-#define OPENGL_AA_POINT   (1<<2)
-#define OPENGL_AA_LINE    (1<<3)
-#define OPENGL_AA_POLYGON (1<<4)
-#define gl_has(f)         (gl_screen.flags & (f)) // Check for the flag.
+#define OPENGL_FULLSCREEN   (1<<0)
+#define OPENGL_DOUBLEBUF    (1<<1)
+#define OPENGL_AA_POINT     (1<<2)
+#define OPENGL_AA_LINE      (1<<3)
+#define OPENGL_AA_POLYGON   (1<<4)
+#define OPENGL_FRAG_SHADER  (1<<5)
+#define OPENGL_VERT_SHADER  (1<<6)
+#define gl_has(f)           (gl_screen.flags & (f)) // Check for the flag.
 typedef struct glInfo_ {
   int w, h;         // Window dimensions.
   int depth;        // Depth in bpp.