Fix non uniform scaling where out_w > in_w && out_h < in_h.

stb_resample.h

@@ -432,7 +432,7 @@ static float* stbr__add_empty_ring_buffer_entry(stbr__info* stbr_info, int n)
 	return ring_buffer;
 }
 
-static void stbr__resample_horizontal_upsample(stbr__info* stbr_info, int n)
+static void stbr__resample_horizontal_upsample(stbr__info* stbr_info, int n, float* output_buffer)
 {
 	STBR_UNIMPLEMENTED(stbr_info->output_w < stbr_info->input_w);
 	int x, k, c;
@@ -443,8 +443,6 @@ static void stbr__resample_horizontal_upsample(stbr__info* stbr_info, int n)
 	stbr__contributors* horizontal_contributors = stbr_info->horizontal_contributors;
 	float* horizontal_coefficients = stbr_info->horizontal_coefficients;
 
-	float* ring_buffer = stbr__add_empty_ring_buffer_entry(stbr_info, n);
-
 	for (x = 0; x < output_w; x++)
 	{
 		int n0 = horizontal_contributors[x].n0;
@@ -466,7 +464,11 @@ static void stbr__resample_horizontal_upsample(stbr__info* stbr_info, int n)
 				continue;
 
 			for (c = 0; c < channels; c++)
-				ring_buffer[out_texel_index + c] += decode_buffer[in_texel_index + c] * coefficient;
+			{
+				output_buffer[out_texel_index + c] += decode_buffer[in_texel_index + c] * coefficient;
+
+				STBR_DEBUG_ASSERT(output_buffer[out_texel_index + c] <= 1.0f);
+			}
 		}
 	}
 }
@@ -483,9 +485,7 @@ static void stbr__resample_horizontal_downsample(stbr__info* stbr_info, int n)
 
 	float* horizontal_buffer = stbr_info->horizontal_buffer;
 
-	STBR_DEBUG_ASSERT(stbr_info->output_h < stbr_info->input_h);
-
-	memset(horizontal_buffer, 0, stbr_info->output_w * channels * sizeof(float));
+	STBR_DEBUG_ASSERT(stbr_info->output_w < stbr_info->input_w);
 
 	for (x = 0; x < input_w; x++)
 	{
@@ -529,7 +529,7 @@ static void stbr__decode_and_resample_upsample(stbr__info* stbr_info, int n)
 	stbr__decode_scanline(stbr_info, n);
 
 	// Now resample it into the ring buffer.
-	stbr__resample_horizontal_upsample(stbr_info, n);
+	stbr__resample_horizontal_upsample(stbr_info, n, stbr__add_empty_ring_buffer_entry(stbr_info, n));
 
 	// Now it's sitting in the ring buffer ready to be used as source for the vertical sampling.
 }
@@ -545,8 +545,13 @@ static void stbr__decode_and_resample_downsample(stbr__info* stbr_info, int n)
 	// Decode the nth scanline from the source image into the decode buffer.
 	stbr__decode_scanline(stbr_info, n);
 
+	memset(stbr_info->horizontal_buffer, 0, stbr_info->output_w * stbr_info->channels * sizeof(float));
+
 	// Now resample it into the horizontal buffer.
-	stbr__resample_horizontal_downsample(stbr_info, n);
+	if (stbr_info->output_w > stbr_info->input_w)
+		stbr__resample_horizontal_upsample(stbr_info, n, stbr_info->horizontal_buffer);
+	else
+		stbr__resample_horizontal_downsample(stbr_info, n);
 
 	// Now it's sitting in the horizontal buffer ready to be distributed into the ring buffers.
 }
@@ -638,7 +643,7 @@ static void stbr__resample_vertical_downsample(stbr__info* stbr_info, int n, int
 	int n0 = vertical_contributors->n0;
 	int n1 = vertical_contributors->n1;
 
-	STBR_DEBUG_ASSERT(stbr_info->output_w < stbr_info->input_w);
+	STBR_DEBUG_ASSERT(stbr_info->output_h < stbr_info->input_h);
 	STBR_DEBUG_ASSERT(n0 >= in_first_scanline);
 	STBR_DEBUG_ASSERT(n1 <= in_last_scanline);