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author | Gregory Nutt <gnutt@nuttx.org> | 2014-12-05 13:02:44 -0600 |
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committer | Gregory Nutt <gnutt@nuttx.org> | 2014-12-05 13:02:44 -0600 |
commit | e340b784cc39934935a5267a91f34e7443f2d21c (patch) | |
tree | 1173a46159a13e0373a95151c8447bdc6a7f8eff /apps/graphics/traveler/src/trv_raycntl.c | |
parent | af493a338db96e3150ab8c2923fc9dbeb025a04d (diff) | |
download | nuttx-e340b784cc39934935a5267a91f34e7443f2d21c.tar.gz nuttx-e340b784cc39934935a5267a91f34e7443f2d21c.tar.bz2 nuttx-e340b784cc39934935a5267a91f34e7443f2d21c.zip |
Add third of several ray cast/rendering files
Diffstat (limited to 'apps/graphics/traveler/src/trv_raycntl.c')
-rw-r--r-- | apps/graphics/traveler/src/trv_raycntl.c | 805 |
1 files changed, 805 insertions, 0 deletions
diff --git a/apps/graphics/traveler/src/trv_raycntl.c b/apps/graphics/traveler/src/trv_raycntl.c new file mode 100644 index 000000000..f1f8b1cec --- /dev/null +++ b/apps/graphics/traveler/src/trv_raycntl.c @@ -0,0 +1,805 @@ +/******************************************************************************* + * apps/graphics/traveler/src/trv_raycntl.c + * This file contains the high-level ray caster control logic + * + * Copyright (C) 2014 Gregory Nutt. All rights reserved. + * Author: Gregory Nutt <gnutt@nuttx.org> + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in + * the documentation and/or other materials provided with the + * distribution. + * 3. Neither the name NuttX nor the names of its contributors may be + * used to endorse or promote products derived from this software + * without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS + * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE + * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, + * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS + * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED + * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN + * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE + * POSSIBILITY OF SUCH DAMAGE. + * + ****************************************************************************/ + +/**************************************************************************** + * Included files + ****************************************************************************/ + +#include "trv_types.h" +#include "trv_debug.h" +#include "trv_world.h" +#include "trv_plane.h" +#include "trv_bitmaps.h" +#include "trv_paltable.h" +#include "trv_trigtbl.h" +#include "trv_graphics.h" +#include "trv_pov.h" +#include "trv_rayrend.h" +#include "trv_rayprune.h" +#include "trv_raycast.h" +#include "trv_raycntl.h" + +/**************************************************************************** + * Pre-processor Definitions + ****************************************************************************/ + +/* These definitions simplify creation of the initial ray casting cell */ + +#define TOP_HEIGHT (VGULP_SIZE/2) +#define BOT_HEIGHT (VGULP_SIZE - TOP_HEIGHT + 1) + +#define TOP_ROW 0 +#define MID_ROW (TOP_ROW + TOP_HEIGHT - 1) +#define BOT_ROW (VGULP_SIZE-1) + +#define LEFT_WIDTH ((HGULP_SIZE+1)/2) +#define RIGHT_WIDTH (HGULP_SIZE - LEFT_WIDTH + 2) + +#define LEFT_COL 0 +#define MID_COL (LEFT_COL + LEFT_WIDTH - 1) +#define RIGHT_COL HGULP_SIZE + +/* The following macro converts a g_yaw[] array index into a relative screen + * yaw. This is used by the ray caster to perform view corrections. + */ + +#define RELYAW(i) (((i) + WINDOW_LEFT) - (WINDOW_WIDTH/2)) + +/* Macro to determine if two hits "hit" the same object */ + +#define SAME_CELL(i1,j1,i2,j2) \ + (g_ray_hit[i1][j1].rect == g_ray_hit[i2][j2].rect) + +/**************************************************************************** + * Public Data + ****************************************************************************/ + +/* The following array describes the hits from X/Y/Z-ray casting for the + * current HGULP_SIZE x VGULP_SIZE cell + */ + +struct trv_raycast_s g_ray_hit[VGULP_SIZE][HGULP_SIZE + 1]; + +/* This array points to the screen buffer row corresponding to the + * pitch angle + */ + +FAR uint8_t *g_buffer_row[VGULP_SIZE]; + +/* The is the "column" offset in g_buffer_row for the current cell being + * operated on. This value is updated in a loop by trv_raycaster. */ + +int16_t g_cell_column; + +/* This structure holds the parameters used in the current ray cast */ + +struct trv_camera_s g_camera; + +/**************************************************************************** + * Private Data + ****************************************************************************/ + +/* These are all of the yaw angles which will be used by the ray caster + * on a given cycle + */ + +static int16_t g_yaw[IMAGE_WIDTH + 1]; + +/* These are all of the pitch angles which will be used by the ray caster + * on each horizontal pass of a given cycle + */ + +static int16_t g_pitch[VGULP_SIZE]; + +/**************************************************************************** + * Private Functions + ****************************************************************************/ + +/**************************************************************************** + * Function: trv_resolve_cell + * + * Description: + * If the hits in the corners of the input cell are not the same, then + * recursively resolve the cell until all four corners are the same. + * When the are the same, then rend the cell to the display buffer. + * + ***************************************************************************/ + +static void trv_resolve_cell(uint8_t toprow, uint8_t leftcol, + uint8_t height, uint8_t width) +{ + uint8_t midrow; + uint8_t botrow; + uint8_t midcol; + uint8_t rightcol; + uint8_t topheight; + uint8_t botheight; + uint8_t leftwidth; + uint8_t rightwidth; + + /* Check if the cell has been reduced to a vertical line */ + + if (width > 1) + { + /* No.. Check if the cell has been reduce to a horizontal line */ + + if (height > 1) + { + /* No.. It is still a rectangular region. Check if the top half hit + * the same cell type + */ + + if (!SAME_CELL(toprow, leftcol, toprow, (leftcol + width - 1))) + { + /* No.. the top corners are different. Compare the top left and + * bottom left corners to decide how to divide this up + */ + + if (!SAME_CELL(toprow, leftcol, (toprow + height - 1), leftcol)) + { + /* The left corners are not the same. Check the right + * corners. + */ + + if (!SAME_CELL(toprow, (leftcol + width - 1), + (toprow + height - 1), (leftcol + width - 1))) + { + /* The right corners are not the same either. Divide the + * cell into three cells, retaining the bottom half + * (whose corners might be the same). + */ + + leftwidth = ((width + 1) >> 1); + if (leftwidth == 1) + { + rightwidth = 1; + midcol = leftcol + 1; + } + else + { + /* The cell is greater than 2 columns in width */ + + rightwidth = width - leftwidth + 1; + midcol = leftcol + leftwidth - 1; + + /* Get the top middle hit */ + + trv_raycast(g_pitch[toprow], + g_yaw[g_cell_column + midcol], + RELYAW(g_cell_column + midcol), + &g_ray_hit[toprow][midcol]); + } + + topheight = ((height + 1) >> 1); + if (topheight == 1) + { + botheight = 1; + midrow = toprow + 1; + } + else + { + /* The cell is greater that 2 rows in height */ + + botheight = height - topheight + 1; + midrow = toprow + topheight - 1; + + /* Get the middle left hit */ + + trv_raycast(g_pitch[midrow], + g_yaw[g_cell_column + leftcol], + RELYAW(g_cell_column + leftcol), + &g_ray_hit[midrow][leftcol]); + + /* Get the center hit */ + + if (rightwidth > 1) + { + trv_raycast(g_pitch[midrow], + g_yaw[g_cell_column + midcol], + RELYAW(g_cell_column + midcol), + &g_ray_hit[midrow][midcol]); + } + + /* Get the middle right hit */ + + rightcol = leftcol + width - 1; + trv_raycast(g_pitch[midrow], + g_yaw[g_cell_column + rightcol], + RELYAW(g_cell_column + rightcol), + &g_ray_hit[midrow][rightcol]); + } + + trv_resolve_cell(toprow, leftcol, topheight, leftwidth); + trv_resolve_cell(toprow, midcol, topheight, rightwidth); + trv_resolve_cell(midrow, leftcol, botheight, width); + } + + /* The left corners are not the same, but the right are. + * Divide the cell into three cells, retaining the right half + */ + + else + { + leftwidth = ((width + 1) >> 1); + if (leftwidth == 1) + { + rightwidth = 1; + midcol = leftcol + 1; + } + else + { + /* The cell is greater than 2 columns in width */ + + rightwidth = width - leftwidth + 1; + midcol = leftcol + leftwidth - 1; + + /* Get the top middle hit */ + + trv_raycast(g_pitch[toprow], + g_yaw[g_cell_column + midcol], + RELYAW(g_cell_column + midcol), + &g_ray_hit[toprow][midcol]); + + /* Get the bottom middle hit */ + + botrow = toprow + height - 1; + trv_raycast(g_pitch[botrow], + g_yaw[g_cell_column + midcol], + RELYAW(g_cell_column + midcol), + &g_ray_hit[botrow][midcol]); + } + + topheight = ((height + 1) >> 1); + if (topheight == 1) + { + botheight = 1; + midrow = toprow + 1; + } + else + { + /* The cell is greater that 2 rows in height */ + + botheight = height - topheight + 1; + midrow = toprow + topheight - 1; + + /* Get the middle left hit */ + + trv_raycast(g_pitch[midrow], + g_yaw[g_cell_column + leftcol], + RELYAW(g_cell_column + leftcol), + &g_ray_hit[midrow][leftcol]); + + /* Get the center hit */ + + if (rightwidth > 1) + { + trv_raycast(g_pitch[midrow], + g_yaw[g_cell_column + midcol], + RELYAW(g_cell_column + midcol), + &g_ray_hit[midrow][midcol]); + } + } + + trv_resolve_cell(toprow, leftcol, topheight, leftwidth); + trv_resolve_cell(midrow, leftcol, botheight, leftwidth); + trv_resolve_cell(toprow, midcol, height, rightwidth); + } + } + + /* The left sides are the same! Divide the cell vertically into + * two cells */ + + else + { + leftwidth = ((width + 1) >> 1); + if (leftwidth == 1) + { + rightwidth = 1; + midcol = leftcol + 1; + } + else + { + /* The cell is greater than 2 columns in width */ + + rightwidth = width - leftwidth + 1; + midcol = leftcol + leftwidth - 1; + + /* Get the top middle hit */ + + trv_raycast(g_pitch[toprow], g_yaw[g_cell_column + midcol], + RELYAW(g_cell_column + midcol), + &g_ray_hit[toprow][midcol]); + + /* Get the bottom middle hit */ + + botrow = toprow + height - 1; + trv_raycast(g_pitch[botrow], g_yaw[g_cell_column + midcol], + RELYAW(g_cell_column + midcol), + &g_ray_hit[botrow][midcol]); + } + + trv_resolve_cell(toprow, leftcol, height, leftwidth); + trv_resolve_cell(toprow, midcol, height, rightwidth); + } + } + + /* The top corners are the same. Compare the top left and bottom + * left corners + */ + + else if (!SAME_CELL(toprow, leftcol, (toprow + height - 1), leftcol)) + { + /* The top corners are the same, but left corners are not. Divide + * the cell into two cells horizontally + */ + + topheight = ((height + 1) >> 1); + if (topheight == 1) + { + botheight = 1; + midrow = toprow + 1; + } + else + { + /* The cell is greater that 2 rows in height */ + + botheight = height - topheight + 1; + midrow = toprow + topheight - 1; + + /* Get the middle left hit */ + + trv_raycast(g_pitch[midrow], g_yaw[g_cell_column + leftcol], + RELYAW(g_cell_column + leftcol), + &g_ray_hit[midrow][leftcol]); + + /* Get the middle right hit */ + + rightcol = leftcol + width - 1; + trv_raycast(g_pitch[midrow], g_yaw[g_cell_column + rightcol], + RELYAW(g_cell_column + rightcol), + &g_ray_hit[midrow][rightcol]); + } + + trv_resolve_cell(toprow, leftcol, topheight, width); + trv_resolve_cell(midrow, leftcol, botheight, width); + } + + /* The top and left corners are the same. Check the lower right + * corner + */ + + else if (!SAME_CELL(toprow, leftcol, (toprow + height - 1), (leftcol + width - 1))) + { + /* The lower right corner differs from all of the others. Divide + * the cell into three cells, retaining the left half + */ + + leftwidth = ((width + 1) >> 1); + if (leftwidth == 1) + { + rightwidth = 1; + midcol = leftcol + 1; + } + else + { + /* The cell is greater than 2 columns in width */ + + rightwidth = width - leftwidth + 1; + midcol = leftcol + leftwidth - 1; + + /* Get the top middle hit */ + + trv_raycast(g_pitch[toprow], g_yaw[g_cell_column + midcol], + RELYAW(g_cell_column + midcol), + &g_ray_hit[toprow][midcol]); + + /* Get the bottom middle hit */ + + botrow = toprow + height - 1; + trv_raycast(g_pitch[botrow], g_yaw[g_cell_column + midcol], + RELYAW(g_cell_column + midcol), + &g_ray_hit[botrow][midcol]); + } + + topheight = ((height + 1) >> 1); + if (topheight == 1) + { + botheight = 1; + midrow = toprow + 1; + } + else + { + /* The cell is greater that 2 rows in height */ + + botheight = height - topheight + 1; + midrow = toprow + topheight - 1; + + /* Get the middle right hit */ + + rightcol = leftcol + width - 1; + trv_raycast(g_pitch[midrow], g_yaw[g_cell_column + rightcol], + RELYAW(g_cell_column + rightcol), + &g_ray_hit[midrow][rightcol]); + + /* Get the center hit */ + + if (rightwidth > 1) + { + trv_raycast(g_pitch[midrow], g_yaw[g_cell_column + midcol], + RELYAW(g_cell_column + midcol), + &g_ray_hit[midrow][midcol]); + } + } + + trv_resolve_cell(toprow, leftcol, height, leftwidth); + trv_resolve_cell(toprow, midcol, topheight, rightwidth); + trv_resolve_cell(midrow, midcol, botheight, rightwidth); + } + + /* The four corners are the same! */ + + else + { + /* Apply texturing */ + + trv_rend_cell(toprow, leftcol, height, width); + } + } + + /* The cell has been reduced to a horizontal line */ + + else + { + /* Check if the endpoints of the horizontal line are the same */ + + if (!SAME_CELL(toprow, leftcol, toprow, (leftcol + width - 1))) + { + /* No.. they are different. Divide the line in half */ + + leftwidth = ((width + 1) >> 1); + if (leftwidth == 1) + { + rightwidth = 1; + midcol = leftcol + 1; + } + else + { + /* The cell is greater than 2 columns in width */ + + rightwidth = width - leftwidth + 1; + midcol = leftcol + leftwidth - 1; + + /* Get the middle hit */ + + trv_raycast(g_pitch[toprow], g_yaw[g_cell_column + midcol], + RELYAW(g_cell_column + midcol), + &g_ray_hit[toprow][midcol]); + } + + trv_resolve_cell(toprow, leftcol, 1, leftwidth); + trv_resolve_cell(toprow, midcol, 1, rightwidth); + } + + /* The endpoints of the horizontal line are the same! */ + + else + { + /* Apply texturing */ + + trv_rend_row(toprow, leftcol, width); + } + } + } + + /* The cell is only 1 pixel wide. Check if it has been reduced to a single + * pixel + */ + + else if (height > 1) + { + /* No.. The cell has been reduced to a vertical line. Check if the + * endpoints are the same. + */ + + if (!SAME_CELL(toprow, leftcol, (toprow + height - 1), leftcol)) + { + /* No.. they are different. Divide the line in half */ + + topheight = ((height + 1) >> 1); + if (topheight == 1) + { + botheight = 1; + midrow = toprow + 1; + } + else + { + /* The cell is greater that 2 rows in height */ + + botheight = height - topheight + 1; + midrow = toprow + topheight - 1; + + /* Get the middle hit */ + + trv_raycast(g_pitch[midrow], g_yaw[g_cell_column + leftcol], + RELYAW(g_cell_column + leftcol), + &g_ray_hit[midrow][leftcol]); + } + + trv_resolve_cell(toprow, leftcol, topheight, 1); + trv_resolve_cell(midrow, leftcol, botheight, 1); + } + + /* The endpoints of the vertical line are the same! */ + + else + { + /* Apply texturing */ + + trv_rend_column(toprow, leftcol, height); + } + } + + /* The cell has been reduced to a single pixel. */ + + else + { + /* Apply texturing */ + + trv_rend_pixel(toprow, leftcol); + } +} + +/**************************************************************************** + * Public Functions + ****************************************************************************/ + +/**************************************************************************** + * Function: trv_raycaster + * + * Description: + * This is the heart of the system. it casts out 320 rays and builds the + * 3-D image from their intersections with the walls. + * + ***************************************************************************/ + +void trv_raycaster(FAR struct trv_camera_s *player, + FAR struct trv_graphics_info_s *ginfo) +{ + int16_t row; /* the current row being cast 0..IMAGE_HEIGHT */ + int16_t yaw; /* Working yaw angle */ + int16_t pitch; /* Working pitch angle */ + uint8_t *buffer; /* Points the screen buffer row for this pitch */ + int i; + + trv_vdebug("\ntrv_raycaster: x=%d y=%d z=%d yaw=%d pitch=%d", + player->x, player->x, player->z, player->yaw, player->pitch); + + /* Copy the input "player" to the working "camera */ + + g_camera = *player; + + /* The horizontal field of view is determined by the width of the window + * (centered at the yaw angle) + */ + + yaw = g_camera.yaw - (IMAGE_WIDTH / 2) + (HGULP_SIZE * VIDEO_COLUMN_ANGLE); + if (yaw < 0) + { + yaw += ANGLE_360; + } + + /* The vertical field of view is determined by the currently active screen + * HEIGHT. NOTE: camera pitch cannot exceed 90 degrees. Not check is + * performed here. + */ + + pitch = g_camera.pitch + (IMAGE_HEIGHT / 2); + if (pitch >= ANGLE_360) + { + pitch -= ANGLE_360; + } + + /* Loop through all columns at each yaw angle on the screen */ + + for (g_cell_column = IMAGE_WIDTH; g_cell_column >= 0; g_cell_column--) + { + /* Save the yaw angle. By saving all of the yaw angles, we can avoid + * complex tests for 360 degree wraps. + */ + + g_yaw[g_cell_column] = yaw; + + /* Test if viewing yaw angle needs to wrap around */ + + yaw += VIDEO_COLUMN_ANGLE; + if (yaw >= ANGLE_360) + { + yaw -= ANGLE_360; + } + } + + /* Seed the algorithm PART I: Set up the raycaster this yaw range. */ + + trv_ray_yawprune(g_yaw[IMAGE_WIDTH], g_yaw[0]); + + /* Top of Ray Casting Loops */ + + /* Point to the first row of the rending buffer. This will be bumped to + * successive rows with each change in the pitch angle. + */ + + buffer = &ginfo->swbuffer[IMAGE_TOP]; + + /* Loop through each row at each pitch angle */ + + for (row = 0; (row < (IMAGE_HEIGHT - VGULP_SIZE + 1)); row += VGULP_SIZE) + { + /* Initialize the pitch angles that will be needed in the inner loop. + * These are pre-calculated so that once we get started, we need not have + * to be concerned about zero crossing conditions. + */ + + g_pitch[0] = pitch; + g_buffer_row[0] = &buffer[IMAGE_LEFT]; + + for (i = 1; i < VGULP_SIZE; i++) + { + g_pitch[i] = g_pitch[i - 1] - VIDEO_ROW_ANGLE; + if (g_pitch[i] < ANGLE_0) + { + g_pitch[i] += ANGLE_360; + } + + g_buffer_row[i] = g_buffer_row[i - 1] + TRV_SCREEN_WIDTH; + } + + /* Seed the algorithm PART II: Set up the raycaster for this horizontal + * swathe + */ + + trv_ray_pitchprune(g_pitch[VGULP_SIZE - 1], g_pitch[0]); + + /* Seed the algorithm PART III: These initial hits will be moved to the + * beginning the hit array on the first pass through the loop. + */ + + trv_raycast(g_pitch[TOP_ROW], g_yaw[IMAGE_WIDTH], + RELYAW(IMAGE_WIDTH), &g_ray_hit[TOP_ROW][LEFT_COL]); + trv_raycast(g_pitch[BOT_ROW], g_yaw[IMAGE_WIDTH], + RELYAW(IMAGE_WIDTH), &g_ray_hit[BOT_ROW][LEFT_COL]); + + /* Loop through all columns at each yaw angle on the screen window */ + + for (g_cell_column = (IMAGE_WIDTH - HGULP_SIZE + 1); + g_cell_column >= 0; g_cell_column -= HGULP_SIZE) + { + trv_vdebug("\ng_cell_column=%d yaw=%d", g_cell_column, + g_yaw[g_cell_column]); + + /* Perform Ray VGULP_SIZE x HGULP_SIZE Casting */ + + /* The hits at the right corners will be the same as the hits for for + * the left hand corners on the next pass */ + + g_ray_hit[TOP_ROW][RIGHT_COL] = g_ray_hit[TOP_ROW][LEFT_COL]; + g_ray_hit[BOT_ROW][RIGHT_COL] = g_ray_hit[BOT_ROW][LEFT_COL]; + + /* Now get new hits in the right corners. */ + + trv_raycast(g_pitch[TOP_ROW], g_yaw[g_cell_column], + RELYAW(g_cell_column), &g_ray_hit[TOP_ROW][LEFT_COL]); + trv_raycast(g_pitch[BOT_ROW], g_yaw[g_cell_column], + RELYAW(g_cell_column), &g_ray_hit[BOT_ROW][LEFT_COL]); + + /* Now, resolve the cell recursively until the hits are the same in + * all four corners */ + + trv_resolve_cell(TOP_ROW, LEFT_COL, VGULP_SIZE, (HGULP_SIZE + 1)); + } + + /* End of the pitch loop. Bump up the pitch angle and the rending buffer + * pointer for the next time through the outer loop */ + + pitch -= (VGULP_SIZE * VIDEO_ROW_ANGLE); + if (pitch < ANGLE_0) + { + pitch += ANGLE_360; + } + + buffer += (VGULP_SIZE * TRV_SCREEN_WIDTH); + + /* Inform the ray cast engine that we are done with this horizonatal + * swathe. + */ + + trv_ray_pitchunprune(); + } + + /* Inform the ray cast engine that we are done. */ + + trv_ray_yawunprune(); +} + +/**************************************************************************** + * Function: trv_get_texture + * + * Description: + * This function returns the cell texture at the current cell row and + * column. This function is used by the texture rending functions when + * processing a cell on a transparent wall and a transparent pixel is + * encountered. This is a very inefficient way to handle these cases! + * Prevention of this condition is the best approach. However, total + * elimination of the condition is impossible. + * + ***************************************************************************/ + +uint8_t trv_get_texture(uint8_t row, uint8_t col) +{ + FAR struct trv_raycast_s *ptr = &g_ray_hit[row][col]; + FAR uint8_t *palptr; + int16_t zone; + + /* Perform a ray cast to get the hit at this row & column */ + + trv_raycast(g_pitch[row], g_yaw[g_cell_column + col], + RELYAW(g_cell_column + col), ptr); + + /* Check if we hit anything */ + + if (ptr->rect) + { + /* Get a pointer to the palette map to use on this pixel */ + + if (IS_SHADED(ptr->rect)) + { + zone = GET_ZONE(ptr->xdist, ptr->ydist); + palptr = GET_PALPTR(zone); + } + else + { + palptr = GET_PALPTR(0); + } + + /* We did, return the pixel at this location */ + /* PROBLEM: Need to know if the is an even or odd hit */ + + return palptr[GET_FRONT_PIXEL(ptr->rect, ptr->xpos, ptr->ypos)]; + } + else + { + return INVISIBLE_PIXEL; + } +} |