From: Steinar H. Gunderson <sgunderson@bigfoot.com>
Date: Sun, 6 Sep 2015 22:10:48 +0000 (+0200)
Subject: Minor optimization in ResampleEffect: Set less GL state.
X-Git-Tag: 1.2.0~25
X-Git-Url: https://git.sesse.net/?p=movit;a=commitdiff_plain;h=c2ca57b71bf77244acc85aaccb2d6c360517c5a3

Minor optimization in ResampleEffect: Set less GL state.

In particular, if we can avoid it, use glTexSubImage2D instead of glTexImage2D.
This actually has a real effect, at least on Intel/Linux, where the drive seems
to stall on some mappings.

Of course, this only really helps for things like pans, not zooms.
---

diff --git a/resample_effect.cpp b/resample_effect.cpp
index 54eec86..0ec611a 100644
--- a/resample_effect.cpp
+++ b/resample_effect.cpp
@@ -380,7 +380,8 @@ SingleResamplePassEffect::SingleResamplePassEffect(ResampleEffect *parent)
 	  last_output_width(-1),
 	  last_output_height(-1),
 	  last_offset(0.0 / 0.0),  // NaN.
-	  last_zoom(0.0 / 0.0)  // NaN.
+	  last_zoom(0.0 / 0.0),  // NaN.
+	  last_texture_width(-1), last_texture_height(-1)
 {
 	register_int("direction", (int *)&direction);
 	register_int("input_width", &input_width);
@@ -554,16 +555,39 @@ void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const str
 	check_error();
 	glBindTexture(GL_TEXTURE_2D, texnum);
 	check_error();
-	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
-	check_error();
-	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
-	check_error();
-	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
-	check_error();
+	if (last_texture_width == -1) {
+		// Need to set this state the first time.
+		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+		check_error();
+		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
+		check_error();
+		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
+		check_error();
+	}
+
+	GLenum type, internal_format;
+	void *pixels;
 	if (fallback_to_fp32) {
-		glTexImage2D(GL_TEXTURE_2D, 0, GL_RG32F, src_bilinear_samples, dst_samples, 0, GL_RG, GL_FLOAT, bilinear_weights_fp32);
+		type = GL_FLOAT;
+		internal_format = GL_RG32F;
+		pixels = bilinear_weights_fp32;
+	} else {
+		type = GL_HALF_FLOAT;
+		internal_format = GL_RG16F;
+		pixels = bilinear_weights_fp16;
+	}
+
+	if (int(src_bilinear_samples) == last_texture_width &&
+	    int(dst_samples) == last_texture_height &&
+	    internal_format == last_texture_internal_format) {
+		// Texture dimensions and type are unchanged; it is more efficient
+		// to just update it rather than making an entirely new texture.
+		glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, src_bilinear_samples, dst_samples, GL_RG, type, pixels);
 	} else {
-		glTexImage2D(GL_TEXTURE_2D, 0, GL_RG16F, src_bilinear_samples, dst_samples, 0, GL_RG, GL_HALF_FLOAT, bilinear_weights_fp16);
+		glTexImage2D(GL_TEXTURE_2D, 0, internal_format, src_bilinear_samples, dst_samples, 0, GL_RG, type, pixels);
+		last_texture_width = src_bilinear_samples;
+		last_texture_height = dst_samples;
+		last_texture_internal_format = internal_format;
 	}
 	check_error();
 
diff --git a/resample_effect.h b/resample_effect.h
index 669d15b..73dfc21 100644
--- a/resample_effect.h
+++ b/resample_effect.h
@@ -109,6 +109,8 @@ private:
 	float last_offset, last_zoom;
 	int src_bilinear_samples, num_loops;
 	float slice_height;
+	int last_texture_width, last_texture_height;
+	GLuint last_texture_internal_format;
 };
 
 }  // namespace movit