rtl/gfx: implement fragment shading

5 files changed, 123 insertions, 7 deletions

diff --git a/rtl/gfx/gfx_defs.sv b/rtl/gfx/gfx_defs.sv
index cc6e6f3..429928c 100644
--- a/rtl/gfx/gfx_defs.sv
+++ b/rtl/gfx/gfx_defs.sv
@@ -38,9 +38,13 @@ typedef logic[19:0] half_coord;
 `define GFX_Y_RES      480
 `define GFX_LINEAR_RES (`GFX_X_RES * `GFX_Y_RES)
 
+`define COLOR_CHANNELS 4
+
+typedef logic[7:0] color8;
+
 typedef struct packed
 {
-	logic[7:0] r, g, b;
+	color8 r, g, b;
 } rgb24;
 
 typedef struct packed
@@ -50,13 +54,14 @@ typedef struct packed
 
 typedef struct packed
 {
-	logic[7:0] a, r, g, b;
+	color8 a, r, g, b;
 } rgb32;
 
 `define FIXED_FRAC 16
 
 `define FIXED_FMA_STAGES     5
 `define FIXED_FMA_DOT_STAGES (2 * `FIXED_FMA_STAGES)
+`define LERP_STAGES          `FIXED_FMA_DOT_STAGES
 
 typedef logic signed[31:0] fixed;
 typedef fixed[2:0]         fixed_tri;
@@ -119,6 +124,7 @@ typedef struct packed
 
 typedef frag_xy[`GFX_FINE_LANES - 1:0] frag_xy_lanes;
 typedef logic[`GFX_FINE_LANES - 1:0]   paint_lanes;
+typedef fixed[`COLOR_CHANNELS - 1:0]   color_lerp_lanes;
 
 typedef struct packed
 {
@@ -126,6 +132,7 @@ typedef struct packed
 	rgb32        color;
 } frag_paint;
 
-`define GFX_FRAG_ADDR_STAGES 3
+`define GFX_FRAG_ADDR_STAGES  3
+`define GFX_FRAG_SHADE_STAGES (`LERP_STAGES + 1)
 
 `endif
diff --git a/rtl/gfx/gfx_frag.sv b/rtl/gfx/gfx_frag.sv
index 3598ed9..b4481ce 100644
--- a/rtl/gfx/gfx_frag.sv
+++ b/rtl/gfx/gfx_frag.sv
@@ -27,7 +27,7 @@ module gfx_frag
 
 	logic addr_ready, addr_stall;
 
-	gfx_pipeline_flow #(.STAGES(`GFX_FRAG_ADDR_STAGES)) addr_flow
+	gfx_pipeline_flow #(.STAGES(`GFX_FRAG_SHADE_STAGES)) addr_flow
 	(
 		.stall(addr_stall),
 		.in_ready(addr_ready),
@@ -37,12 +37,36 @@ module gfx_frag
 		.*
 	);
 
+	linear_coord linear;
+
 	gfx_frag_addr addr
 	(
+		.frag(funnel_frag),
 		.stall(addr_stall),
+		.*
+	);
 
-		.frag(funnel_frag),
-		.linear(),
+	localparam ADDR_WAIT_Z_STAGES = `GFX_FRAG_SHADE_STAGES - `GFX_FRAG_ADDR_STAGES;
+
+	gfx_pipes #(.WIDTH($bits(linear_coord)), .DEPTH(ADDR_WAIT_Z_STAGES)) addr_pipes
+	(
+		.in(linear),
+		.out(),
+		.stall(addr_stall),
+		.*
+	);
+
+	gfx_frag_shade shade
+	(
+		.stall(addr_stall),
+
+		.b1(),
+		.b2(),
+		.color(),
+
+		.argb0(),
+		.argb1_argb0(),
+		.argb2_argb0(),
 		.*
 	);
 
diff --git a/rtl/gfx/gfx_frag_addr.sv b/rtl/gfx/gfx_frag_addr.sv
index 9b817cb..23bd315 100644
--- a/rtl/gfx/gfx_frag_addr.sv
+++ b/rtl/gfx/gfx_frag_addr.sv
@@ -17,7 +17,7 @@ module gfx_frag_addr
 	 *
 	 *   linear = y_corregido * `GFX_X_RES + x_corregido
 	 *
-	 * Afortunadamente, esto es trivializable y no necesita FMA:
+	 * Afortunadamente, esto no necesita una FMA, como procederé a demostrar:
 	 *
 	 *   y * `GFX_X_RES + x
 	 * = y * 640 + x
diff --git a/rtl/gfx/gfx_frag_shade.sv b/rtl/gfx/gfx_frag_shade.sv
new file mode 100644
index 0000000..d2ad7ce
--- /dev/null
+++ b/rtl/gfx/gfx_frag_shade.sv
@@ -0,0 +1,53 @@
+`include "gfx/gfx_defs.sv"
+
+module gfx_frag_shade
+(
+	input  logic            clk,
+
+	input  fixed            b1,
+	                        b2,
+	input  color_lerp_lanes argb0,
+	                        argb1_argb0,
+	                        argb2_argb0,
+	input  logic            stall,
+
+	output rgb32            color
+);
+
+	struct packed
+	{
+		logic                                    sign;
+		logic[$bits(fixed) - `FIXED_FRAC - 2:0]  out_of_range;
+		color8                                   color;
+		logic[`FIXED_FRAC - $bits(color8) - 1:0] sub;
+	} lerped[`COLOR_CHANNELS];
+
+	fixed channel_lerp[`COLOR_CHANNELS];
+	color8[`COLOR_CHANNELS - 1:0] out;
+
+	assign color = out;
+
+	genvar i;
+	generate
+		for (i = 0; i < `COLOR_CHANNELS; ++i) begin: channels
+			assign lerped[i] = channel_lerp[i];
+
+			gfx_lerp lerp
+			(
+				.q(channel_lerp[i]),
+				.q0(argb0[i]),
+				.q1_q0(argb1_argb0[i]),
+				.q2_q0(argb2_argb0[i]),
+				.*
+			);
+
+			always_ff @(posedge clk)
+				if (!stall) begin
+					out[i] <= lerped[i].color;
+					if (lerped[i].sign || |lerped[i].out_of_range)
+						out[i] <= {($bits(color8)){!lerped[i].sign}};
+				end
+		end
+	endgenerate
+
+endmodule
diff --git a/rtl/gfx/gfx_lerp.sv b/rtl/gfx/gfx_lerp.sv
new file mode 100644
index 0000000..42e4393
--- /dev/null
+++ b/rtl/gfx/gfx_lerp.sv
@@ -0,0 +1,32 @@
+`include "gfx/gfx_defs.sv"
+
+module gfx_lerp
+(
+	input  logic clk,
+
+	input  fixed b1,
+	             b2,
+				 q0,
+	             q1_q0,
+	             q2_q0,
+	input  logic stall,
+
+	output fixed q
+);
+
+	/* Interpolación lineal, trivializada.
+	 *
+	 * Esta es la clave: https://fgiesen.wordpress.com/2013/02/06/the-barycentric-conspirac/
+	 */
+
+	gfx_fixed_fma_dot fma
+	(
+		.c(q0),
+		.a0(b1),
+		.b0(q1_q0),
+		.a1(b2),
+		.b1(q2_q0),
+		.*
+	);
+
+endmodule