gsdx-ogl: DATE with texture barrier

Much faster for small batch that write the alpha value. Code can
be enabled with accurate_date option.

Here a summary of all DATE possibilities:
1/ no overlap of primitive
    => texture barrier (pro no setup of stencil and single draw)

2/ alpha written
    => small batch => texture barrier (primitive by primitive). Done in N-primitive draw calls.
    (based on GL_ARB_texture_barrier)

    => bigger batch => compute the first good primitive, slow but only 2 draw calls.
    (based on GL_ARB_shader_image_load_store)

    => Otherwise there is the UserHacks_AlphaStencil but it is a hack!

3/ alpha written
    => full setup of stencil ( 2 draw calls)

plugins/GSdx/GLLoader.cpp

@@ -504,13 +504,6 @@ namespace GLLoader {
 				theApp.SetConfig("accurate_blend", 0);
 			}
 		}
-		if (!found_GL_ARB_shader_image_load_store) {
-			if (theApp.GetConfig("accurate_date", 0)) {
-				fprintf(stderr, "Error GL_ARB_shader_image_load_store is not supported by your driver so you can't enable accurate_date! Sorry.\n");
-				theApp.SetConfig("accurate_date", 0);
-			}
-		}
-
 
 		fprintf(stderr, "\n");
 

plugins/GSdx/GSRendererOGL.cpp

@@ -198,6 +198,9 @@ void GSRendererOGL::SendDraw(bool require_barrier)
 		ASSERT(m_vt.m_primclass != GS_LINE_CLASS);
 		ASSERT(GLLoader::found_geometry_shader);
 
+		GL_INS("Special Draw");
+
+		// FIXME: Investigate: do a dynamic check to pack as many primitives as possibles
 		size_t nb_vertex = (m_vt.m_primclass == GS_TRIANGLE_CLASS) ? 3 : 2;
 
 		for (size_t p = 0; p < m_index.tail; p += nb_vertex) {
@@ -278,8 +281,17 @@ void GSRendererOGL::DrawPrims(GSTexture* rt, GSTexture* ds, GSTextureCache::Sour
 		if (GLLoader::found_GL_ARB_texture_barrier && !PrimitiveOverlap()) {
 			DATE_GL45 = true;
 			DATE = false;
-		} else if (om_csel.wa && (!context->TEST.ATE || context->TEST.ATST == ATST_ALWAYS)) {
-			DATE_GL42 = m_accurate_date && GLLoader::found_GL_ARB_shader_image_load_store && !UserHacks_AlphaStencil;
+		} else if (m_accurate_date && !UserHacks_AlphaStencil &&
+				om_csel.wa && (!context->TEST.ATE || context->TEST.ATST == ATST_ALWAYS)) {
+			// texture barrier will split the draw call into n draw call. It is very efficient for
+			// few primitive draws. Otherwise it sucks.
+			if (GLLoader::found_GL_ARB_texture_barrier && (m_index.tail < 100)) {
+				require_barrier = true;
+				DATE_GL45 = true;
+				DATE = false;
+			} else {
+				DATE_GL42 = GLLoader::found_GL_ARB_shader_image_load_store;
+			}
 		}
 	}
 

plugins/GSdx/res/glsl/tfx_fs.glsl

@@ -419,16 +419,24 @@ void ps_main()
 	// Pixel with alpha equal to 1 will failed
 	float rt_a = texelFetch(RtSampler, ivec2(gl_FragCoord.xy), 0).a;
 	if ((127.5f / 255.0f) < rt_a) { // < 0x80 pass (== 0x80 should not pass)
+#if PS_DATE >= 5
+		discard;
+#else
 		imageStore(img_prim_min, ivec2(gl_FragCoord.xy), ivec4(-1));
 		return;
+#endif
 	}
 #elif (PS_DATE & 3) == 2 && !defined(DISABLE_GL42_image)
 	// DATM == 1
 	// Pixel with alpha equal to 0 will failed
 	float rt_a = texelFetch(RtSampler, ivec2(gl_FragCoord.xy), 0).a;
 	if(rt_a < (127.5f / 255.0f)) { // >= 0x80 pass
+#if PS_DATE >= 5
+		discard;
+#else
 		imageStore(img_prim_min, ivec2(gl_FragCoord.xy), ivec4(-1));
 		return;
+#endif
 	}
 #endif
 

plugins/GSdx/res/glsl_source.h

@@ -1133,16 +1133,24 @@ static const char* tfx_fs_all_glsl =
 	"	// Pixel with alpha equal to 1 will failed\n"
 	"	float rt_a = texelFetch(RtSampler, ivec2(gl_FragCoord.xy), 0).a;\n"
 	"	if ((127.5f / 255.0f) < rt_a) { // < 0x80 pass (== 0x80 should not pass)\n"
+	"#if PS_DATE >= 5\n"
+	"		discard;\n"
+	"#else\n"
 	"		imageStore(img_prim_min, ivec2(gl_FragCoord.xy), ivec4(-1));\n"
 	"		return;\n"
+	"#endif\n"
 	"	}\n"
 	"#elif (PS_DATE & 3) == 2 && !defined(DISABLE_GL42_image)\n"
 	"	// DATM == 1\n"
 	"	// Pixel with alpha equal to 0 will failed\n"
 	"	float rt_a = texelFetch(RtSampler, ivec2(gl_FragCoord.xy), 0).a;\n"
 	"	if(rt_a < (127.5f / 255.0f)) { // >= 0x80 pass\n"
+	"#if PS_DATE >= 5\n"
+	"		discard;\n"
+	"#else\n"
 	"		imageStore(img_prim_min, ivec2(gl_FragCoord.xy), ivec4(-1));\n"
 	"		return;\n"
+	"#endif\n"
 	"	}\n"
 	"#endif\n"
 	"\n"