TEV: store raster color output in a TEV register

mardy · WinterMute · commit d89ccf9aba7b · 2024-11-16T11:28:23.000Z
The GX_CC_RASC and GX_CA_RASA constants do not refer to the untextured
vertex color, but only to the color being generated by the color channel
associated with the current stage: while in some situation these two
entities coincide, in the case of a lit object we do have two active
color channels, and these constants can only be used to refer to one of
them at a time. Furthermore, when we enter the texturing stage on a lit
geometry, we pass GX_COLORNULL, meaning that no rasterizer color channel
is associated, and here GX_CC_RASC and GX_CA_RASA only render black.

Yet, the texture environment operations in OpenGL sometimes need to
operate on the color emitted on the vertex by the rasterizer.

The solution is to emit the result of the lighting operations not on
GX_TEVPREV (which gets changed at each stage), but on a well-named
register (one of GX_TEVREG0 - GX_TEVREG2), which later stages can
then refer to.
diff --git a/src/gc_gl.c b/src/gc_gl.c
@@ -2041,6 +2041,14 @@ static void setup_fog()
 
 bool _ogx_setup_render_stages()
 {
+    u8 raster_output, raster_reg_index;
+    if (glparamstate.texture_enabled) {
+        raster_reg_index = _ogx_gpu_resources->tevreg_first++;
+        raster_output = GX_TEVREG0 + raster_reg_index;
+    } else {
+        raster_output = GX_TEVPREV;
+    }
+
     if (glparamstate.lighting.enabled) {
         LightMasks light_mask = prepare_lighting();
 
@@ -2135,14 +2143,14 @@ bool _ogx_setup_render_stages()
         GX_SetTevColorIn(GX_TEVSTAGE1, GX_CC_CPREV, GX_CC_ZERO, GX_CC_ZERO, GX_CC_RASC);
         GX_SetTevAlphaIn(GX_TEVSTAGE1, GX_CA_ZERO, GX_CA_APREV, GX_CA_RASA, GX_CA_ZERO);
         // Operation: Sum a + d
-        GX_SetTevColorOp(GX_TEVSTAGE1, GX_TEV_ADD, GX_TB_ZERO, GX_CS_SCALE_1, GX_TRUE, GX_TEVPREV);
-        GX_SetTevAlphaOp(GX_TEVSTAGE1, GX_TEV_ADD, GX_TB_ZERO, GX_CS_SCALE_1, GX_TRUE, GX_TEVPREV);
+        GX_SetTevColorOp(GX_TEVSTAGE1, GX_TEV_ADD, GX_TB_ZERO, GX_CS_SCALE_1, GX_TRUE, raster_output);
+        GX_SetTevAlphaOp(GX_TEVSTAGE1, GX_TEV_ADD, GX_TB_ZERO, GX_CS_SCALE_1, GX_TRUE, raster_output);
         // Select COLOR1A1 for the rasterizer, disable all textures
         GX_SetTevOrder(GX_TEVSTAGE1, GX_TEXCOORDNULL, GX_TEXMAP_DISABLE, GX_COLOR1A1);
 
         if (glparamstate.texture_enabled) {
-            // Do not select any raster value, Texture 0 for texture rasterizer and TEXCOORD0 slot for tex coordinates
-            _ogx_setup_texture_stages(GX_CC_CPREV, GX_CA_APREV, GX_COLORNULL);
+            // Do not select any raster color channel
+            _ogx_setup_texture_stages(raster_reg_index, GX_COLORNULL);
         }
     } else {
         // Unlit scene
@@ -2167,7 +2175,7 @@ bool _ogx_setup_render_stages()
 
         if (glparamstate.texture_enabled) {
             // Select COLOR0A0 for the rasterizer, Texture 0 for texture rasterizer and TEXCOORD0 slot for tex coordinates
-            _ogx_setup_texture_stages(GX_CC_RASC, GX_CA_RASA, GX_COLOR0A0);
+            _ogx_setup_texture_stages(raster_reg_index, GX_COLOR0A0);
         } else {
             // Use one stage only
             _ogx_gpu_resources->tevstage_first += 1;
diff --git a/src/texture_unit.c b/src/texture_unit.c
@@ -78,7 +78,8 @@ typedef struct {
 } TevSource;
 
 static TevSource gl_rgbsource_to_gx(GLenum source, GLenum operand,
-                                    u8 prev_rgb, u8 prev_alpha)
+                                    u8 prev_rgb, u8 prev_alpha,
+                                    u8 raster_rgb, u8 raster_alpha)
 {
     TevSource ret = { GX_CC_ZERO, false };
     if (operand == GL_ONE_MINUS_SRC_COLOR) {
@@ -105,16 +106,16 @@ static TevSource gl_rgbsource_to_gx(GLenum source, GLenum operand,
     case GL_CONSTANT: ret.source = GX_CC_KONST; break;
     case GL_PRIMARY_COLOR:
         switch (operand) {
-        case GL_SRC_COLOR: ret.source = GX_CC_RASC; break;
-        case GL_SRC_ALPHA: ret.source = GX_CC_RASA; break;
+        case GL_SRC_COLOR: ret.source = raster_rgb; break;
+        case GL_SRC_ALPHA: ret.source = raster_alpha; break;
         }
         break;
     }
     return ret;
 }
 
 static TevSource gl_alphasource_to_gx(GLenum source, GLenum operand,
-                                      u8 prev_alpha)
+                                      u8 prev_alpha, u8 raster_alpha)
 {
     TevSource ret = { GX_CA_ZERO, false };
     /* For the alpha channel, operand can only be either GL_SRC_ALPHA or
@@ -127,7 +128,7 @@ static TevSource gl_alphasource_to_gx(GLenum source, GLenum operand,
     case GL_TEXTURE: ret.source = GX_CA_TEXA; break;
     case GL_PREVIOUS: ret.source = prev_alpha; break;
     case GL_CONSTANT: ret.source = GX_CA_KONST; break;
-    case GL_PRIMARY_COLOR: ret.source = GX_CA_RASA; break;
+    case GL_PRIMARY_COLOR: ret.source = raster_alpha; break;
     }
     return ret;
 }
@@ -339,28 +340,21 @@ static TevInput compute_tev_input(GLenum combine_func, u8 stage, GXColor color,
     return ret;
 }
 
-static void setup_combine_operation(const OgxTextureUnit *te,
-                                    u8 stage)
+static void setup_combine_operation(const OgxTextureUnit *te, u8 stage,
+                                    u8 prev_rgb, u8 prev_alpha,
+                                    u8 raster_rgb, u8 raster_alpha)
 {
     TevSource source_rgb[3];
     TevSource source_alpha[3];
 
-    u8 prev_rgb, prev_alpha;
-    if (stage == GX_TEVSTAGE0) {
-       prev_rgb = GX_CC_RASC;
-       prev_alpha = GX_CA_RASA;
-    } else {
-       prev_rgb = GX_CC_CPREV;
-       prev_alpha = GX_CA_APREV;
-    }
-
     for (int i = 0; i < 3; i++) {
         source_rgb[i] = gl_rgbsource_to_gx(te->source_rgb[i],
                                            te->operand_rgb[i],
-                                           prev_rgb, prev_alpha);
+                                           prev_rgb, prev_alpha,
+                                           raster_rgb, raster_alpha);
         source_alpha[i] = gl_alphasource_to_gx(te->source_alpha[i],
                                                te->operand_alpha[i],
-                                               prev_alpha);
+                                               prev_alpha, raster_alpha);
     }
 
     TevInput rgb = compute_tev_input(te->combine_rgb, stage, te->color,
@@ -379,7 +373,8 @@ static void setup_combine_operation(const OgxTextureUnit *te,
 
 static void setup_texture_stage(const OgxTextureUnit *tu,
                                 u8 stage, u8 tex_coord, u8 tex_map,
-                                u8 raster_color, u8 raster_alpha,
+                                u8 prev_rgb, u8 prev_alpha,
+                                u8 raster_rgb, u8 raster_alpha,
                                 u8 channel)
 {
     switch (tu->mode) {
@@ -391,25 +386,26 @@ static void setup_texture_stage(const OgxTextureUnit *tu,
     case GL_ADD:
         /* In data: d: Texture Color a: raster value, Operation: a+d
          * Alpha gets multiplied. */
-        GX_SetTevColorIn(stage, raster_color, GX_CC_ZERO, GX_CC_ZERO, GX_CC_TEXC);
-        GX_SetTevAlphaIn(stage, GX_CA_ZERO, raster_alpha, GX_CA_TEXA, GX_CA_ZERO);
+        GX_SetTevColorIn(stage, prev_rgb, GX_CC_ZERO, GX_CC_ZERO, GX_CC_TEXC);
+        GX_SetTevAlphaIn(stage, GX_CA_ZERO, prev_alpha, GX_CA_TEXA, GX_CA_ZERO);
         break;
     case GL_BLEND:
         /* In data: c: Texture Color, a: raster value, b: tex env
          * Operation: a(1-c)+b*c
          * Until we implement GL_TEXTURE_ENV_COLOR, use white (GX_CC_ONE) for
          * the tex env color. */
-        GX_SetTevColorIn(stage, raster_color, GX_CC_ONE, GX_CC_TEXC, GX_CC_ZERO);
-        GX_SetTevAlphaIn(stage, GX_CA_ZERO, raster_alpha, GX_CA_TEXA, GX_CA_ZERO);
+        GX_SetTevColorIn(stage, prev_rgb, GX_CC_ONE, GX_CC_TEXC, GX_CC_ZERO);
+        GX_SetTevAlphaIn(stage, GX_CA_ZERO, prev_alpha, GX_CA_TEXA, GX_CA_ZERO);
         break;
     case GL_COMBINE:
-        setup_combine_operation(tu, stage);
+        setup_combine_operation(tu, stage, prev_rgb, prev_alpha,
+                                raster_rgb, raster_alpha);
         break;
     case GL_MODULATE:
     default:
         // In data: c: Texture Color b: raster value, Operation: b*c
-        GX_SetTevColorIn(stage, GX_CC_ZERO, raster_color, GX_CC_TEXC, GX_CC_ZERO);
-        GX_SetTevAlphaIn(stage, GX_CA_ZERO, raster_alpha, GX_CA_TEXA, GX_CA_ZERO);
+        GX_SetTevColorIn(stage, GX_CC_ZERO, prev_rgb, GX_CC_TEXC, GX_CC_ZERO);
+        GX_SetTevAlphaIn(stage, GX_CA_ZERO, prev_alpha, GX_CA_TEXA, GX_CA_ZERO);
         break;
     }
     if (!tu->mode != GL_COMBINE) {
@@ -437,9 +433,20 @@ static void setup_texture_stage_matrix(const OgxTextureUnit *tu,
     GX_LoadTexMtxImm(m, dtt_matrix, GX_MTX3x4);
 }
 
-void _ogx_setup_texture_stages(u8 raster_color, u8 raster_alpha,
-                               u8 channel)
+void _ogx_setup_texture_stages(u8 raster_reg_index, u8 channel)
 {
+    u8 raster_rgb, raster_alpha;
+    if (channel != GX_COLORNULL) {
+        raster_rgb = GX_CC_RASC;
+        raster_alpha = GX_CA_RASA;
+    } else {
+        raster_rgb = GX_CC_C0 + raster_reg_index * 2;
+        raster_alpha = GX_CA_A0 + raster_reg_index;
+    }
+
+    u8 prev_rgb = raster_rgb;
+    u8 prev_alpha = raster_alpha;
+
     /* This variable holds the number of enabled texture units for which the
      * client provided texture coordinates (not generated, but literally a
      * GX_VA_TEX* array was specified). */
@@ -466,7 +473,8 @@ void _ogx_setup_texture_stages(u8 raster_color, u8 raster_alpha,
         u8 dtt_matrix = GX_DTTMTX0 + _ogx_gpu_resources->dttmtx_first++ * 3;
 
         setup_texture_stage(tu, stage, tex_coord, tex_map,
-                            raster_color, raster_alpha, channel);
+                            prev_rgb, prev_alpha,
+                            raster_rgb, raster_alpha, channel);
 
         setup_texture_stage_matrix(tu, dtt_matrix);
         if (tu->gen_enabled) {
@@ -478,7 +486,7 @@ void _ogx_setup_texture_stages(u8 raster_color, u8 raster_alpha,
 
         /* All texture stages after the first one get their vertex color from
          * the previous stage */
-        raster_color = GX_CC_CPREV;
-        raster_alpha = GX_CA_APREV;
+        prev_rgb = GX_CC_CPREV;
+        prev_alpha = GX_CA_APREV;
     }
 }
diff --git a/src/texture_unit.h b/src/texture_unit.h
@@ -36,8 +36,7 @@ POSSIBILITY OF SUCH DAMAGE.
 extern "C" {
 #endif
 
-void _ogx_setup_texture_stages(u8 raster_color, u8 raster_alpha,
-                               u8 channel);
+void _ogx_setup_texture_stages(u8 raster_reg_index, u8 channel);
 
 #ifdef __cplusplus
 } // extern C
