From 3a36e34bd2b4e374bc501606ec28111eb3822334 Mon Sep 17 00:00:00 2001
From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
Date: Thu, 20 Mar 2014 21:16:49 +0100
Subject: [PATCH] Do not glReadPixels() with type GL_RED.

GLES can only read RGBA pixels. Downconvert ourselves when we need to.
---
 init.cpp      | 16 ++++++++--------
 test_util.cpp | 30 ++++++++++++++++++++++++++++--
 2 files changed, 36 insertions(+), 10 deletions(-)

diff --git a/init.cpp b/init.cpp
index 89998f4..c5e8113 100644
--- a/init.cpp
+++ b/init.cpp
@@ -122,14 +122,14 @@ void measure_texel_subpixel_precision()
 	// Now read the data back and see what the card did.
 	// (We only look at the red channel; the others will surely be the same.)
 	// We assume a linear ramp; anything else will give sort of odd results here.
-	float out_data[width];
-	glReadPixels(0, 0, width, 1, GL_RED, GL_FLOAT, out_data);
+	float out_data[width * 4];
+	glReadPixels(0, 0, width, 1, GL_RGBA, GL_FLOAT, out_data);
 	check_error();
 
 	float biggest_jump = 0.0f;
 	for (unsigned i = 1; i < width; ++i) {
-		assert(out_data[i] >= out_data[i - 1]);
-		biggest_jump = max(biggest_jump, out_data[i] - out_data[i - 1]);
+		assert(out_data[i * 4] >= out_data[(i - 1) * 4]);
+		biggest_jump = max(biggest_jump, out_data[i * 4] - out_data[(i - 1) * 4]);
 	}
 
 	assert(biggest_jump > 0.0);
@@ -242,16 +242,16 @@ void measure_roundoff_problems()
 
 	// Now read the data back and see what the card did. (Ignore the last value.)
 	// (We only look at the red channel; the others will surely be the same.)
-	unsigned char out_data[512];
-	glReadPixels(0, 0, 512, 1, GL_RED, GL_UNSIGNED_BYTE, out_data);
+	unsigned char out_data[512 * 4];
+	glReadPixels(0, 0, 512, 1, GL_RGBA, GL_UNSIGNED_BYTE, out_data);
 	check_error();
 
 	int wrongly_rounded = 0;
 	for (unsigned i = 0; i < 255; ++i) {
-		if (out_data[i * 2 + 0] != i) {
+		if (out_data[(i * 2 + 0) * 4] != i) {
 			++wrongly_rounded;
 		}
-		if (out_data[i * 2 + 1] != i + 1) {
+		if (out_data[(i * 2 + 1) * 4] != i + 1) {
 			++wrongly_rounded;
 		}
 	}
diff --git a/test_util.cpp b/test_util.cpp
index f48ff7f..a5cd44c 100644
--- a/test_util.cpp
+++ b/test_util.cpp
@@ -132,7 +132,20 @@ void EffectChainTester::run(float *out_data, GLenum format, Colorspace color_spa
 	chain.render_to_fbo(fbo, width, height);
 
 	glBindFramebuffer(GL_FRAMEBUFFER, fbo);
-	glReadPixels(0, 0, width, height, format, GL_FLOAT, out_data);
+	check_error();
+	if (!epoxy_is_desktop_gl() && format == GL_RED) {
+		// GLES will only read GL_RGBA.
+		float *temp = new float[width * height * 4];
+		glReadPixels(0, 0, width, height, GL_RGBA, GL_FLOAT, temp);
+		check_error();
+		for (int i = 0; i < width * height; ++i) {
+			out_data[i] = temp[i * 4];
+		}
+		delete[] temp;
+	} else {
+		glReadPixels(0, 0, width, height, format, GL_FLOAT, out_data);
+		check_error();
+	}
 
 	if (format == GL_RGBA) {
 		width *= 4;
@@ -150,7 +163,20 @@ void EffectChainTester::run(unsigned char *out_data, GLenum format, Colorspace c
 	chain.render_to_fbo(fbo, width, height);
 
 	glBindFramebuffer(GL_FRAMEBUFFER, fbo);
-	glReadPixels(0, 0, width, height, format, GL_UNSIGNED_BYTE, out_data);
+	check_error();
+	if (!epoxy_is_desktop_gl() && format == GL_RED) {
+		// GLES will only read GL_RGBA.
+		unsigned char *temp = new unsigned char[width * height * 4];
+		glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, temp);
+		check_error();
+		for (int i = 0; i < width * height; ++i) {
+			out_data[i] = temp[i * 4];
+		}
+		delete[] temp;
+	} else {
+		glReadPixels(0, 0, width, height, format, GL_UNSIGNED_BYTE, out_data);
+		check_error();
+	}
 
 	if (format == GL_RGBA) {
 		width *= 4;
-- 
2.39.2