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Optimized the interpolate_texcoords() function:
Use fast approximation to log(). Check for dq==0 to avoid a per-pixel divide.
This commit is contained in:
Brian Paul
parent
8baae48fb7
commit
c14a5a6c62
1 changed files with 148 additions and 38 deletions
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@ -1,4 +1,4 @@
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/* $Id: s_span.c,v 1.34 2002/02/15 16:27:13 brianp Exp $ */
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/* $Id: s_span.c,v 1.35 2002/02/17 01:49:31 brianp Exp $ */
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/*
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* Mesa 3-D graphics library
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@ -262,8 +262,58 @@ interpolate_z(GLcontext *ctx, struct sw_span *span)
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}
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/*
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* Return log_base_2(x) / 2.
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* We divide by two here since we didn't square rho in the triangle function.
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*/
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#ifdef USE_IEEE
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/* Fill in the span.texcoords array from the interpolation values */
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#if 0
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/* This is pretty fast, but not accurate enough (only 2 fractional bits).
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* Based on code from http://www.stereopsis.com/log2.html
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*/
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static INLINE GLfloat HALF_LOG2(GLfloat x)
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{
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const GLfloat y = x * x * x * x;
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const GLuint ix = *((GLuint *) &y);
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const GLuint exp = (ix >> 23) & 0xFF;
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const GLint log2 = ((GLint) exp) - 127;
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return (GLfloat) log2 * (0.5 / 4.0); /* 4, because of x^4 above */
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}
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#endif
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/* Pretty fast, and accurate.
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* Based on code from http://www.flipcode.com/totd/
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*/
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static INLINE GLfloat HALF_LOG2(GLfloat val)
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{
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GLint *exp_ptr = (GLint *) &val;
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GLint x = *exp_ptr;
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const GLint log_2 = ((x >> 23) & 255) - 128;
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x &= ~(255 << 23);
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x += 127 << 23;
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*exp_ptr = x;
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val = ((-1.0f/3) * val + 2) * val - 2.0f/3;
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return 0.5F * (val + log_2);
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}
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#else /* USE_IEEE */
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/* Slow, portable solution.
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* NOTE: log_base_2(x) = log(x) / log(2)
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* NOTE: 1.442695 = 1/log(2).
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*/
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#define HALF_LOG2(x) ((GLfloat) (log(x) * (1.442695F * 0.5F)))
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#endif /* USE_IEEE */
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/*
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* Fill in the span.texcoords array from the interpolation values.
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* XXX We could optimize here for the case when dq = 0. That would
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* usually be the case when using an orthographic projection.
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*/
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static void
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interpolate_texcoords(GLcontext *ctx, struct sw_span *span)
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{
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@ -275,6 +325,7 @@ interpolate_texcoords(GLcontext *ctx, struct sw_span *span)
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GLuint u;
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for (u = 0; u < ctx->Const.MaxTextureUnits; u++) {
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if (ctx->Texture.Unit[u]._ReallyEnabled) {
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const GLfloat rho = span->rho[u];
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const GLfloat ds = span->texStep[u][0];
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const GLfloat dt = span->texStep[u][1];
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const GLfloat dr = span->texStep[u][2];
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@ -284,17 +335,32 @@ interpolate_texcoords(GLcontext *ctx, struct sw_span *span)
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GLfloat r = span->tex[u][2];
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GLfloat q = span->tex[u][3];
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GLuint i;
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for (i = 0; i < span->end; i++) {
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if (dq == 0.0) {
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/* Ortho projection or polygon's parallel to window X axis */
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const GLfloat invQ = (q == 0.0F) ? 1.0F : (1.0F / q);
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span->texcoords[u][i][0] = s * invQ;
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span->texcoords[u][i][1] = t * invQ;
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span->texcoords[u][i][2] = r * invQ;
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span->lambda[u][i] = (GLfloat)
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(log(span->rho[u] * invQ * invQ) * 1.442695F * 0.5F);
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s += ds;
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t += dt;
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r += dr;
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q += dq;
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const GLfloat lambda = HALF_LOG2(rho * invQ * invQ);
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for (i = 0; i < span->end; i++) {
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span->texcoords[u][i][0] = s * invQ;
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span->texcoords[u][i][1] = t * invQ;
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span->texcoords[u][i][2] = r * invQ;
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span->lambda[u][i] = lambda;
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s += ds;
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t += dt;
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r += dr;
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}
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}
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else {
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for (i = 0; i < span->end; i++) {
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const GLfloat invQ = (q == 0.0F) ? 1.0F : (1.0F / q);
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span->texcoords[u][i][0] = s * invQ;
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span->texcoords[u][i][1] = t * invQ;
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span->texcoords[u][i][2] = r * invQ;
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span->lambda[u][i] = HALF_LOG2(rho * invQ * invQ);
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s += ds;
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t += dt;
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r += dr;
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q += dq;
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}
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}
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}
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}
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@ -314,15 +380,29 @@ interpolate_texcoords(GLcontext *ctx, struct sw_span *span)
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GLfloat r = span->tex[u][2];
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GLfloat q = span->tex[u][3];
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GLuint i;
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for (i = 0; i < span->end; i++) {
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if (dq == 0.0) {
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/* Ortho projection or polygon's parallel to window X axis */
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const GLfloat invQ = (q == 0.0F) ? 1.0F : (1.0F / q);
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span->texcoords[u][i][0] = s * invQ;
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span->texcoords[u][i][1] = t * invQ;
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span->texcoords[u][i][2] = r * invQ;
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s += ds;
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t += dt;
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r += dr;
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q += dq;
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for (i = 0; i < span->end; i++) {
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span->texcoords[u][i][0] = s * invQ;
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span->texcoords[u][i][1] = t * invQ;
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span->texcoords[u][i][2] = r * invQ;
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s += ds;
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t += dt;
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r += dr;
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}
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}
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else {
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for (i = 0; i < span->end; i++) {
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const GLfloat invQ = (q == 0.0F) ? 1.0F : (1.0F / q);
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span->texcoords[u][i][0] = s * invQ;
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span->texcoords[u][i][1] = t * invQ;
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span->texcoords[u][i][2] = r * invQ;
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s += ds;
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t += dt;
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r += dr;
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q += dq;
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}
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}
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}
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}
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@ -331,6 +411,7 @@ interpolate_texcoords(GLcontext *ctx, struct sw_span *span)
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else {
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if (span->interpMask & SPAN_LAMBDA) {
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/* just texture unit 0, with lambda */
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const GLfloat rho = span->rho[0];
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const GLfloat ds = span->texStep[0][0];
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const GLfloat dt = span->texStep[0][1];
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const GLfloat dr = span->texStep[0][2];
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@ -340,17 +421,32 @@ interpolate_texcoords(GLcontext *ctx, struct sw_span *span)
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GLfloat r = span->tex[0][2];
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GLfloat q = span->tex[0][3];
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GLuint i;
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for (i = 0; i < span->end; i++) {
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if (dq == 0.0) {
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/* Ortho projection or polygon's parallel to window X axis */
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const GLfloat invQ = (q == 0.0F) ? 1.0F : (1.0F / q);
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span->texcoords[0][i][0] = s * invQ;
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span->texcoords[0][i][1] = t * invQ;
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span->texcoords[0][i][2] = r * invQ;
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span->lambda[0][i] = (GLfloat)
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(log(span->rho[0] * invQ * invQ) * 1.442695F * 0.5F);
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s += ds;
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t += dt;
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r += dr;
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q += dq;
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const GLfloat lambda = HALF_LOG2(rho * invQ * invQ);
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for (i = 0; i < span->end; i++) {
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span->texcoords[0][i][0] = s * invQ;
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span->texcoords[0][i][1] = t * invQ;
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span->texcoords[0][i][2] = r * invQ;
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span->lambda[0][i] = lambda;
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s += ds;
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t += dt;
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r += dr;
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}
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}
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else {
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for (i = 0; i < span->end; i++) {
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const GLfloat invQ = (q == 0.0F) ? 1.0F : (1.0F / q);
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span->texcoords[0][i][0] = s * invQ;
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span->texcoords[0][i][1] = t * invQ;
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span->texcoords[0][i][2] = r * invQ;
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span->lambda[0][i] = HALF_LOG2(rho * invQ * invQ);
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s += ds;
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t += dt;
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r += dr;
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q += dq;
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}
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}
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span->arrayMask |= SPAN_LAMBDA;
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}
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@ -365,15 +461,29 @@ interpolate_texcoords(GLcontext *ctx, struct sw_span *span)
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GLfloat r = span->tex[0][2];
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GLfloat q = span->tex[0][3];
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GLuint i;
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for (i = 0; i < span->end; i++) {
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if (dq == 0.0) {
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/* Ortho projection or polygon's parallel to window X axis */
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const GLfloat invQ = (q == 0.0F) ? 1.0F : (1.0F / q);
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span->texcoords[0][i][0] = s * invQ;
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span->texcoords[0][i][1] = t * invQ;
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span->texcoords[0][i][2] = r * invQ;
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s += ds;
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t += dt;
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r += dr;
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q += dq;
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for (i = 0; i < span->end; i++) {
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span->texcoords[0][i][0] = s * invQ;
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span->texcoords[0][i][1] = t * invQ;
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span->texcoords[0][i][2] = r * invQ;
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s += ds;
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t += dt;
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r += dr;
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}
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}
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else {
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for (i = 0; i < span->end; i++) {
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const GLfloat invQ = (q == 0.0F) ? 1.0F : (1.0F / q);
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span->texcoords[0][i][0] = s * invQ;
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span->texcoords[0][i][1] = t * invQ;
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span->texcoords[0][i][2] = r * invQ;
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s += ds;
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t += dt;
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r += dr;
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q += dq;
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}
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}
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}
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}
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