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 54eec864fe7a6c272fa68e3476dfcdf52b31c8a7..0ec611af75bd9bff87e85837410387816e5f9e5a 100644 (file)
--- 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 669d15b94569626d5b1a2bfc058b98162dd6f6be..73dfc210e9732388e193ed2dcd0eb6cdb31d50a8 100644 (file)
--- 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