Remove a very old and outdated comment.

[movit] / effect_chain.h

diff --git a/effect_chain.h b/effect_chain.h
index 22f0b96c6e4eabc807c8bf57a75b70516c3a8cda..918769b3872451576f329a5252568fc214889a03 100644 (file)
--- a/effect_chain.h
+++ b/effect_chain.h
@@ -99,6 +99,19 @@ enum OutputOrigin {
        OUTPUT_ORIGIN_TOP_LEFT,
 };
 
+// Transformation to apply (if any) to pixel data in temporary buffers.
+// See set_intermediate_format() below for more information.
+enum FramebufferTransformation {
+       // The default; just store the value. This is what you usually want.
+       NO_FRAMEBUFFER_TRANSFORMATION,
+
+       // If the values are in linear light, store sqrt(x) to the framebuffer
+       // instead of x itself, of course undoing it with x² on read. Useful as
+       // a rough approximation to the sRGB curve. (If the values are not in
+       // linear light, just store them as-is.)
+       SQUARE_ROOT_FRAMEBUFFER_TRANSFORMATION,
+};
+
 // A node in the graph; basically an effect and some associated information.
 class Node {
 public:
@@ -277,6 +290,46 @@ public:
                this->output_origin = output_origin;
        }
 
+       // Set intermediate format for framebuffers used when we need to bounce
+       // to a temporary texture. The default, GL_RGBA16F, is good for most uses;
+       // it is precise, has good range, and is relatively efficient. However,
+       // if you need even more speed and your chain can do with some loss of
+       // accuracy, you can change the format here (before calling finalize).
+       // Calculations between bounce buffers are still in 32-bit floating-point
+       // no matter what you specify.
+       //
+       // Of special interest is GL_SRGB8_ALPHA8, which stores sRGB-encoded RGB
+       // and linear alpha; this is half the memory bandwidth og GL_RGBA16F,
+       // while retaining reasonable precision for typical image data. It will,
+       // however, cause some gamut clipping if your colorspace is far from sRGB,
+       // as it cannot represent values outside [0,1]. NOTE: If you construct
+       // a chain where you end up bouncing pixels in non-linear light
+       // (gamma different from GAMMA_LINEAR), this will be the wrong thing.
+       // However, it's hard to see how this could happen in a non-contrived
+       // chain; few effects ever need texture bounce or resizing without also
+       // combining multiple pixels, which really needs linear light and thus
+       // triggers a conversion before the bounce.
+       //
+       // If you don't need alpha (or can do with very little of it), GL_RGB10_A2
+       // is even better, as it has two more bits for each color component. There
+       // is no GL_SRGB10, unfortunately, so on its own, it is somewhat worse than
+       // GL_SRGB8, but you can set <transformation> to SQUARE_ROOT_FRAMEBUFFER_TRANSFORMATION,
+       // and sqrt(x) will be stored instead of x. This is a rough approximation to
+       // the sRGB curve, and reduces maximum error (in sRGB distance) by almost an
+       // order of magnitude, well below what you can get from 8-bit true sRGB.
+       // (Note that this strategy avoids the problem with bounced non-linear data
+       // above, since the square root is turned off in that case.) However, texture
+       // filtering will happen on the transformed values, so if you have heavy
+       // downscaling or the likes (e.g. mipmaps), you could get subtly bad results.
+       // You'll need to see which of the two that works the best for you in practice.
+       void set_intermediate_format(
+               GLenum intermediate_format,
+               FramebufferTransformation transformation = NO_FRAMEBUFFER_TRANSFORMATION)
+       {
+               this->intermediate_format = intermediate_format;
+               this->intermediate_transformation = transformation;
+       }
+
        void finalize();
 
        // Measure the GPU time used for each actual phase during rendering.
@@ -288,7 +341,6 @@ public:
        void reset_phase_timing();
        void print_phase_timing();
 
-       //void render(unsigned char *src, unsigned char *dst);
        void render_to_screen()
        {
                render_to_fbo(0, 0, 0);
@@ -438,6 +490,8 @@ private:
        std::vector<Input *> inputs;  // Also contained in nodes.
        std::vector<Phase *> phases;
 
+       GLenum intermediate_format;
+       FramebufferTransformation intermediate_transformation;
        unsigned num_dither_bits;
        OutputOrigin output_origin;
        bool finalized;