drewcassidy/quicktex
1
0
Fork 0
mirror of https://github.com/drewcassidy/quicktex.git synced 2024-09-13 06:37:34 +00:00
Code Issues Projects Releases Activity

add some notes on how the covariance model works

Browse Source
This commit is contained in:
Andrew Cassidy 2021-02-21 03:26:40 -08:00
parent 148d32e28c
commit 9e2e9fba4c
1 changed files with 5 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
src/BC1/BC1Encoder.cpp
View File

@ -317,7 +317,7 @@ void BC1Encoder::FindEndpoints(Color4x4 pixels, BC1Encoder::Flags flags, const B
std::array<Vector4, 16> colors;
Vector4 axis = {306, 601, 117}; // I think this is luma?
Vector4 axis = {306, 601, 117}; // Luma vector
Matrix4x4 covariance;
const unsigned total_power_iters = (flags & Flags::Use6PowerIters) != Flags::None ? 6 : 4;
@ -341,8 +341,10 @@ void BC1Encoder::FindEndpoints(Color4x4 pixels, BC1Encoder::Flags flags, const B
if (covariance[0][2] < 0) delta[0] = -delta[0]; // r vs b
if (covariance[1][2] < 0) delta[1] = -delta[1]; // g vs b
// using the covariance matrix, iteratively stretch the delta vector towards the primary axis of the data
for (unsigned power_iter = 0; power_iter < total_power_iters; power_iter++) { delta = covariance * delta; }
// if we found any correlation, then this is our new axis. otherwise we fallback to the luma vector
float k = delta.MaxAbs(3);
if (k > 2) { axis = delta * (2048.0f / k); }
@ -352,6 +354,8 @@ void BC1Encoder::FindEndpoints(Color4x4 pixels, BC1Encoder::Flags flags, const B
unsigned min_index, max_index;
for (unsigned i = 0; i < 16; i++) {
// since axis is constant here, I dont think its magnitude actually matters,
// since we only care about the min or max dot product
float dot = colors[i].Dot(axis);
if (dot > max_dot) {
max_dot = dot;