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diff --git a/src/mesa/tnl/NOTES b/src/mesa/tnl/NOTES new file mode 100644 index 00000000000..c39b43485eb --- /dev/null +++ b/src/mesa/tnl/NOTES @@ -0,0 +1,102 @@ +INTRODUCTION + +A generic, configurable software implementation of GL transformation & +lighting. + +This module provides an implementation of the routines required by the +'vtxfmt' mechanism of core mesa for tnl functionality in all +combinations of compile and execute modes. + +Most current drivers use the tnl module exclusively to provide this +functionality, though there is an experimental alternate +implementation provided by the tnl_dd/t_dd_imm_* files which can +handle a small subset of GL states in execute mode only. + + +STATE + +To create and destroy the module: + + GLboolean _tnl_CreateContext( GLcontext *ctx ); + void _tnl_DestroyContext( GLcontext *ctx ); + +The module is not active by default, and must be installed by calling +_tnl_Wakeup(). This function installs internal tnl functions into all +the vtxfmt dispatch hooks, thus taking over the task of transformation +and lighting entirely: + + void _tnl_wakeup_exec( GLcontext *ctx ); + void _tnl_wakeup_save_exec( GLcontext *ctx ); + + +This module tracks state changes internally and maintains derived +values based on the current state. For this to work, the driver +ensure the following funciton is called whenever the state changes and +the swsetup module is 'awake': + + void _tnl_InvalidateState( GLcontext *ctx, GLuint new_state ); + +There is no explicit call to put the tnl module to sleep. Simply +install other function pointers into all the vtxfmt dispatch slots, +and (optionally) cease calling _tnl_InvalidateState(). + +CUSTOMIZATION + +The module provides customizability through several mechanisms. The +most important is by allowing drivers to specify the pipeline through +which vertex data is passed, including its eventual transfer to +rasterization hardware (or software). + +The default pipeline is specified in t_pipeline.c, and is usually a +starting point for driver pipelines. Some drivers will remove a stage +where hardware provides support for the implemented operation (for +instance fog where per-pixel hardware fog is available, as in the dri +tdfx driver), or add stages to shortcircuit latter operations (for +example taking advantage of hardware support for strips and other +higher-level primitives (for example the radeon driver). + +In addition, the following functions provide further tweaks: + +extern void +_tnl_need_projected_coords( GLcontext *ctx, GLboolean flag ); + + - Direct the default vertex transformation stage to + produce/not produce projected clip coordinates. + +extern void +_tnl_need_dlist_loopback( GLcontext *ctx, GLboolean flag ); + + - Direct the display list component of the tnl module to + replay display lists as 'glVertex' type calls, rather than + passing the display list data directly into the tnl pipeline + mechanism. + + This allows display lists to be replayed by the tnl module + even when the module is not strictly active. + + +extern void +_tnl_need_dlist_norm_lengths( GLcontext *ctx, GLboolean flag ); + + - Direct the display list component to enable/disable caching + 1/length values for display list normals. Doing so is + ususally helpful when lighting is performed in software, but + wasteful otherwise. + + +DRIVER INTERFACE + +The module itself offers a minimal driver interface: + + void (*RunPipeline)( GLcontext *ctx ); + +Normally this is set to _tnl_RunPipeline(), however the driver can use +this hook to wrap checks or other code around this call. + +In addition, the driver interface for the default render pipeline +stage is housed in the tnl context struct (this could be cleaner). + + +RENDER DRIVER INTERFACE + +See t_context.h for the definition and explanation of this.
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