Manage intermediate textures a bit more efficiently.

By holding on to them only for as long as we need to, we'll save some
peak texture RAM, and _might_ in some situations get a bit less cache
trashing.

diff --git a/effect_chain.cpp b/effect_chain.cpp
index a83a952dfaae331bb5431000823cecefd6b82e7f..c9d746fbafaa390b5cc17437348df0f77e82e87f 100644 (file)
--- a/effect_chain.cpp
+++ b/effect_chain.cpp
@@ -1882,9 +1882,18 @@ void EffectChain::render(GLuint dest_fbo, const vector<DestinationTexture> &dest
 
        set<Phase *> generated_mipmaps;
 
-       // We choose the simplest option of having one texture per output,
-       // since otherwise this turns into an (albeit simple) register allocation problem.
+       // We keep one texture per output, but only for as long as we actually have any
+       // phases that need it as an input. (We don't make any effort to reorder phases
+       // to minimize the number of textures in play, as register allocation can be
+       // complicated and we rarely have much to gain, since our graphs are typically
+       // pretty linear.)
        map<Phase *, GLuint> output_textures;
+       map<Phase *, int> ref_counts;
+       for (Phase *phase : phases) {
+               for (Phase *input : phase->inputs) {
+                       ++ref_counts[input];
+               }
+       }
 
        size_t num_phases = phases.size();
        if (destinations.empty()) {
@@ -1972,6 +1981,15 @@ void EffectChain::render(GLuint dest_fbo, const vector<DestinationTexture> &dest
                if (do_phase_timing) {
                        glEndQuery(GL_TIME_ELAPSED);
                }
+
+               // Drop any input textures we don't need anymore.
+               for (Phase *input : phase->inputs) {
+                       assert(ref_counts[input] > 0);
+                       if (--ref_counts[input] == 0) {
+                               resource_pool->release_2d_texture(output_textures[input]);
+                               output_textures.erase(input);
+                       }
+               }
        }
 
        for (const auto &phase_and_texnum : output_textures) {