From da8dfcce3a52f2de180ead1dd315f6e6cac5fef2 Mon Sep 17 00:00:00 2001
From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
Date: Thu, 3 Apr 2014 23:11:30 +0200
Subject: [PATCH] Rewrite extension checking.

Two big changes:

 1. If you're missing some functionality, Movit will now tell you
    on stderr what you're missing. (We might suppress this later
    if it turns out that people want to init_movit() but are actually
    fine with it failing.)
 2. Use a table instead of repeated if-then logic, since this started
    to become a bit messy after we added OpenGL-version-equivalence
    checks.
---
 init.cpp | 72 +++++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 48 insertions(+), 24 deletions(-)

diff --git a/init.cpp b/init.cpp
index c37614e..a7bd1e3 100644
--- a/init.cpp
+++ b/init.cpp
@@ -278,6 +278,33 @@ void measure_roundoff_problems()
 	check_error();
 }
 
+struct RequiredExtension {
+	int min_equivalent_gl_version;
+	const char extension_name[64];
+};
+const RequiredExtension required_extensions[] = {
+	// We fundamentally need FBOs and floating-point textures.
+	// FBOs are covered by OpenGL 1.5, and are not an extension there.
+	// Floating-point textures are part of OpenGL 3.0 and newer.
+	{ 15, "GL_ARB_framebuffer_object" },
+	{ 30, "GL_ARB_texture_float" },
+
+	// We assume that we can use non-power-of-two textures without restrictions.
+	{ 20, "GL_ARB_texture_non_power_of_two" },
+
+	// We also need GLSL fragment shaders.
+	{ 20, "GL_ARB_fragment_shader" },
+	{ 20, "GL_ARB_shading_language_100" },
+
+	// FlatInput and YCbCrInput uses PBOs. (They could in theory do without,
+	// but no modern card would really not provide it.)
+	{ 21, "GL_ARB_pixel_buffer_object" },
+
+	// ResampleEffect uses RG textures to encode a two-component LUT.
+	// We also need GL_R several places, for single-channel input.
+	{ 30, "GL_ARB_texture_rg" },
+};
+
 bool check_extensions()
 {
 	// GLES generally doesn't use extensions as actively as desktop OpenGL.
@@ -287,37 +314,34 @@ bool check_extensions()
 		if (epoxy_gl_version() >= 30) {
 			movit_srgb_textures_supported = true;
 			movit_shader_rounding_supported = true;
+			return true;
 		} else {
+			fprintf(stderr, "Movit system requirements: GLES version %.1f is too old (GLES 3.0 needed).\n",
+				0.1f * epoxy_gl_version());
+			fprintf(stderr, "Movit initialization failed.\n");
 			return false;
 		}
 	}
 
-	// We fundamentally need FBOs and floating-point textures.
-	// FBOs are covered by OpenGL 1.5, and are not an extension there.
-	// Floating-point textures are part of OpenGL 3.0 and newer.
-	if (epoxy_gl_version() < 15 &&
-	    !epoxy_has_gl_extension("GL_ARB_framebuffer_object")) return false;
-	if (epoxy_gl_version() < 30 &&
-	    !epoxy_has_gl_extension("GL_ARB_texture_float")) return false;
-
-	// We assume that we can use non-power-of-two textures without restrictions.
-	if (epoxy_gl_version() < 20 &&
-	    !epoxy_has_gl_extension("GL_ARB_texture_non_power_of_two")) return false;
-
-	// We also need GLSL fragment shaders.
-	if (epoxy_gl_version() < 20) {
-		if (!epoxy_has_gl_extension("GL_ARB_fragment_shader")) return false;
-		if (!epoxy_has_gl_extension("GL_ARB_shading_language_100")) return false;
+	// Check all extensions, and output errors for the ones that we are missing.
+	bool all_ok = true;
+	int gl_version = epoxy_gl_version();
+
+	for (unsigned i = 0; i < sizeof(required_extensions) / sizeof(required_extensions[0]); ++i) {
+		if (gl_version < required_extensions[i].min_equivalent_gl_version &&
+		    !epoxy_has_gl_extension(required_extensions[i].extension_name)) {
+			fprintf(stderr, "Movit system requirements: Needs extension '%s' or at least OpenGL version %.1f (has version %.1f)\n",
+				required_extensions[i].extension_name,
+				0.1f * required_extensions[i].min_equivalent_gl_version,
+				0.1f * gl_version);
+			all_ok = false;
+		}
 	}
 
-	// FlatInput and YCbCrInput uses PBOs. (They could in theory do without,
-	// but no modern card would really not provide it.)
-	if (epoxy_gl_version() < 21 &&
-	    !epoxy_has_gl_extension("GL_ARB_pixel_buffer_object")) return false;
-
-	// ResampleEffect uses RG textures to encode a two-component LUT.
-	if (epoxy_gl_version() < 30 &&
-	    !epoxy_has_gl_extension("GL_ARB_texture_rg")) return false;
+	if (!all_ok) {
+		fprintf(stderr, "Movit initialization failed.\n");
+		return false;
+	}
 
 	// sRGB texture decode would be nice, but are not mandatory
 	// (GammaExpansionEffect can do the same thing if needed).
-- 
2.39.2