pointAtten: improve measureSize() function

Before, we read one row of pixels where we expected the point to be
in order to compute the point size.  With some drivers single pixel
points might be positioned one above or below the expected position
thus causing the test to fail.  Now, read thee rows of pixels to make
sure we don't miss the point.  The purpose of this test is to measure
attenuated point size, not exact positioning of single pixel points.

1 files changed, 32 insertions, 12 deletions

diff --git a/src/glean/tpointatten.cpp b/src/glean/tpointatten.cpp
index f5ce13e..4ff1c45 100644
--- a/src/glean/tpointatten.cpp
+++ b/src/glean/tpointatten.cpp
@@ -134,16 +134,30 @@ PointAttenuationTest::measureSize(GLfloat yPos) const
 	int x = 0;
 	int y = (int) (yNdc * windowHeight);
 	int w = windowWidth;
-	int h = 1;
-	GLfloat image[windowWidth * 3];
-	// Read row of pixels and add up colors, which should be white
-	// or shades of gray if smoothing is enabled.
-	glReadPixels(x, y, w, h, GL_RGB, GL_FLOAT, image);
-	float sum = 0.0;
-	for (int i = 0; i < w; i++) {
-		sum += (image[i*3+0] + image[i*3+1] + image[i*3+2]) / 3.0;
+	int h = 3;
+	GLfloat image[3 * windowWidth * 3]; // three rows of RGB values
+
+	// Read three row of pixels and add up colors in each row.
+	// Use the row with the greatest sum.  This helps gives us a bit
+	// of leeway in vertical point positioning.
+	// Colors should be white or shades of gray if smoothing is enabled.
+	glReadPixels(x, y - 1, w, h, GL_RGB, GL_FLOAT, image);
+
+	float sum[3] = { 0.0, 0.0, 0.0 };
+	for (int j = 0; j < 3; j++) {
+		for (int i = 0; i < w; i++) {
+			int k = j * 3 * w + i * 3;
+			sum[j] += (image[k+0] + image[k+1] + image[k+2]) / 3.0;
+		}
 	}
-	return sum;
+
+	// find max of the row sums
+	if (sum[0] >= sum[1] && sum[0] >= sum[2])
+		return sum[0];
+	else if (sum[1] >= sum[0] && sum[1] >= sum[2])
+		return sum[1];
+	else
+		return sum[2];
 }
 
 
@@ -152,13 +166,13 @@ PointAttenuationTest::testPointRendering(GLboolean smooth)
 {
 	// epsilon is the allowed size difference in pixels between the
 	// expected and actual rendering.
-	const GLfloat epsilon = smooth ? 1.5 : 1.0;
+	const GLfloat epsilon = (smooth ? 1.5 : 1.0) + 0.0;
 	GLfloat atten[3];
 	int count = 0;
 
 	// Enable front buffer if you want to see the rendering
-	//glDrawBuffer(GL_FRONT);
-	//glReadBuffer(GL_FRONT);
+	glDrawBuffer(GL_FRONT);
+	glReadBuffer(GL_FRONT);
 
 	if (smooth) {
 		glEnable(GL_POINT_SMOOTH);
@@ -192,6 +206,8 @@ PointAttenuationTest::testPointRendering(GLboolean smooth)
 							}
 							glEnd();
 
+									glFinish();
+
 							// test the column of points
 							for (float z = -6.0; z <= 6.0; z += 1.0) {
 								count++;
@@ -205,6 +221,10 @@ PointAttenuationTest::testPointRendering(GLboolean smooth)
 												  expected, actual);
 									return false;
 								}
+								else if(0){
+									printf("pass z=%f exp=%f act=%f\n",
+										   z, expected, actual);
+								}
 							}
 						}
 					}