From: Steinar H. Gunderson <sgunderson@bigfoot.com>
Date: Sat, 27 Oct 2012 19:10:52 +0000 (+0200)
Subject: Factorize the code to compute sampling points for bilinear sampling into a shared... 
X-Git-Tag: 1.0~224
X-Git-Url: https://git.sesse.net/?p=movit;a=commitdiff_plain;h=b09a4cb8dec09bcd1e42026d5b229b57e620e47c

Factorize the code to compute sampling points for bilinear sampling into a shared function, and support negative weights.
---

diff --git a/blur_effect.cpp b/blur_effect.cpp
index 579521f..90d1b68 100644
--- a/blur_effect.cpp
+++ b/blur_effect.cpp
@@ -162,13 +162,8 @@ void SingleBlurPassEffect::set_gl_state(GLuint glsl_program_num, const std::stri
 		float w2 = weight[base_pos + 1];
 
 		float offset, total_weight;
-		if (w1 + w2 < 1e-6) {
-			offset = 0.5f;
-			total_weight = 0.0f;
-		} else {
-			offset = w2 / (w1 + w2);
-			total_weight = w1 + w2;
-		}
+		combine_two_samples(w1, w2, &offset, &total_weight);
+
 		float x = 0.0f, y = 0.0f;
 
 		if (direction == HORIZONTAL) {
diff --git a/util.h b/util.h
index b53bac7..432171a 100644
--- a/util.h
+++ b/util.h
@@ -34,6 +34,22 @@ void print_3x3_matrix(const Eigen::Matrix3d &m);
 // Output a GLSL 3x3 matrix declaration.
 std::string output_glsl_mat3(const std::string &name, const Eigen::Matrix3d &m);
 
+// Calculate where to sample, and with what weight, if one wants to use
+// the GPU's bilinear hardware to sample w1 * x[0] + w2 * x[1].
+static inline void combine_two_samples(float w1, float w2, float *offset, float *total_weight)
+{
+	assert(w1 * w2 >= 0.0f);  // Should not have differing signs.
+	if (fabs(w1 + w2) < 1e-6) {
+		*offset = 0.5f;
+		*total_weight = 0.0f;
+	} else {
+		*offset = w2 / (w1 + w2);
+		*total_weight = w1 + w2;
+	}
+	assert(*offset >= 0.0f);
+	assert(*offset <= 1.0f);
+}
+
 #ifdef NDEBUG
 #define check_error()
 #else