xref: /xsrc/external/mit/libxcvt/dist/lib/libxcvt.c

/*
 * Copyright 2005-2006 Luc Verhaegen.
 * Copyright © 2021 Red Hat, Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 */

/* Standalone VESA CVT standard timing modelines generator. */


#include <string.h>
#include <stdio.h>
#include <stdlib.h>

#include <libxcvt/libxcvt.h>

/*
 * Generate a CVT standard mode from hdisplay, vdisplay and vrefresh.
 *
 * These calculations are stolen from the CVT calculation spreadsheet written
 * by Graham Loveridge. He seems to be claiming no copyright and there seems to
 * be no license attached to this. He apparently just wants to see his name
 * mentioned.
 *
 * This file can be found at http://www.vesa.org/Public/CVT/CVTd6r1.xls
 *
 * Comments and structure corresponds to the comments and structure of the xls.
 * This should ease importing of future changes to the standard (not very
 * likely though).
 *
 * About margins; i'm sure that they are to be the bit between HDisplay and
 * HBlankStart, HBlankEnd and HTotal, VDisplay and VBlankStart, VBlankEnd and
 * VTotal, where the overscan colour is shown. FB seems to call _all_ blanking
 * outside sync "margin" for some reason. Since we prefer seeing proper
 * blanking instead of the overscan colour, and since the Crtc* values will
 * probably get altered after us, we will disable margins altogether. With
 * these calculations, Margins will plainly expand H/VDisplay, and we don't
 * want that. -- libv
 *
 */
struct libxcvt_mode_info *
libxcvt_gen_mode_info(int hdisplay, int vdisplay, float vrefresh, bool reduced, bool interlaced)
{
    bool margins = false;
    float vfield_rate, hperiod;
    int hdisplay_rnd, hmargin;
    int vdisplay_rnd, vmargin, vsync;
    float interlace;            /* Please rename this */
    struct libxcvt_mode_info *mode_info;

    mode_info = calloc(1, sizeof *mode_info);
    if (!mode_info)
        return NULL;

    mode_info->hdisplay = hdisplay;
    mode_info->vdisplay = vdisplay;
    mode_info->vrefresh = vrefresh;

    /* 1) top/bottom margin size (% of height) - default: 1.8 */
#define CVT_MARGIN_PERCENTAGE 1.8

    /* 2) character cell horizontal granularity (pixels) - default 8 */
#define CVT_H_GRANULARITY 8

    /* 4) Minimum vertical front porch (lines) - default 3 */
#define CVT_MIN_V_PORCH_RND 3

    /* 4) Minimum number of vertical back porch lines - default 6 */
#define CVT_MIN_V_BPORCH 6

    /* Pixel Clock step (kHz) */
#define CVT_CLOCK_STEP 250

    /* CVT default is 60.0Hz */
    if (!mode_info->vrefresh)
        mode_info->vrefresh = 60.0;

    /* 1. Required field rate */
    if (interlaced)
        vfield_rate = mode_info->vrefresh * 2;
    else
        vfield_rate = mode_info->vrefresh;

    /* 2. Horizontal pixels */
    hdisplay_rnd = mode_info->hdisplay - (mode_info->hdisplay % CVT_H_GRANULARITY);

    /* 3. Determine left and right borders */
    if (margins) {
        /* right margin is actually exactly the same as left */
        hmargin = (((float) hdisplay_rnd) * CVT_MARGIN_PERCENTAGE / 100.0);
        hmargin -= hmargin % CVT_H_GRANULARITY;
    }
    else {
        hmargin = 0;
    }

    /* 4. Find total active pixels */
    mode_info->hdisplay = hdisplay_rnd + 2 * hmargin;

    /* 5. Find number of lines per field */
    if (interlaced)
        vdisplay_rnd = mode_info->vdisplay / 2;
    else
        vdisplay_rnd = mode_info->vdisplay;

    /* 6. Find top and bottom margins */
    /* nope. */
    if (margins)
        /* top and bottom margins are equal again. */
        vmargin = (((float) vdisplay_rnd) * CVT_MARGIN_PERCENTAGE / 100.0);
    else
        vmargin = 0;

    mode_info->vdisplay = mode_info->vdisplay + 2 * vmargin;

    /* 7. interlace */
    if (interlaced)
        interlace = 0.5;
    else
        interlace = 0.0;

    /* Determine vsync Width from aspect ratio */
    if (!(mode_info->vdisplay % 3) && ((mode_info->vdisplay * 4 / 3) == mode_info->hdisplay))
        vsync = 4;
    else if (!(mode_info->vdisplay % 9) && ((mode_info->vdisplay * 16 / 9) == mode_info->hdisplay))
        vsync = 5;
    else if (!(mode_info->vdisplay % 10) && ((mode_info->vdisplay * 16 / 10) == mode_info->hdisplay))
        vsync = 6;
    else if (!(mode_info->vdisplay % 4) && ((mode_info->vdisplay * 5 / 4) == mode_info->hdisplay))
        vsync = 7;
    else if (!(mode_info->vdisplay % 9) && ((mode_info->vdisplay * 15 / 9) == mode_info->hdisplay))
        vsync = 7;
    else                        /* Custom */
        vsync = 10;

    if (!reduced) {             /* simplified GTF calculation */

        /* 4) Minimum time of vertical sync + back porch interval (µs)
         * default 550.0 */
#define CVT_MIN_VSYNC_BP 550.0

        /* 3) Nominal HSync width (% of line period) - default 8 */
#define CVT_HSYNC_PERCENTAGE 8

        float hblank_percentage;
        int vsync_and_back_porch, vback_porch;
        int hblank, hsync_w;

        /* 8. Estimated Horizontal period */
        hperiod = ((float) (1000000.0 / vfield_rate - CVT_MIN_VSYNC_BP)) /
            (vdisplay_rnd + 2 * vmargin + CVT_MIN_V_PORCH_RND + interlace);

        /* 9. Find number of lines in sync + backporch */
        if (((int) (CVT_MIN_VSYNC_BP / hperiod) + 1) <
            (vsync + CVT_MIN_V_BPORCH))
            vsync_and_back_porch = vsync + CVT_MIN_V_BPORCH;
        else
            vsync_and_back_porch = (int) (CVT_MIN_VSYNC_BP / hperiod) + 1;

        /* 10. Find number of lines in back porch */
        vback_porch = vsync_and_back_porch - vsync;
        (void) vback_porch;

        /* 11. Find total number of lines in vertical field */
        mode_info->vtotal =
            vdisplay_rnd + 2 * vmargin + vsync_and_back_porch + interlace +
            CVT_MIN_V_PORCH_RND;

        /* 5) Definition of Horizontal blanking time limitation */
        /* Gradient (%/kHz) - default 600 */
#define CVT_M_FACTOR 600

        /* Offset (%) - default 40 */
#define CVT_C_FACTOR 40

        /* Blanking time scaling factor - default 128 */
#define CVT_K_FACTOR 128

        /* Scaling factor weighting - default 20 */
#define CVT_J_FACTOR 20

#define CVT_M_PRIME CVT_M_FACTOR * CVT_K_FACTOR / 256
#define CVT_C_PRIME (CVT_C_FACTOR - CVT_J_FACTOR) * CVT_K_FACTOR / 256 + \
        CVT_J_FACTOR

        /* 12. Find ideal blanking duty cycle from formula */
        hblank_percentage = CVT_C_PRIME - CVT_M_PRIME * hperiod / 1000.0;

        /* 13. Blanking time */
        if (hblank_percentage < 20)
            hblank_percentage = 20;

        hblank = mode_info->hdisplay * hblank_percentage / (100.0 - hblank_percentage);
        hblank -= hblank % (2 * CVT_H_GRANULARITY);

        /* 14. Find total number of pixels in a line. */
        mode_info->htotal = mode_info->hdisplay + hblank;

        /* Fill in HSync values */
        mode_info->hsync_end = mode_info->hdisplay + hblank / 2;

        hsync_w = (mode_info->htotal * CVT_HSYNC_PERCENTAGE) / 100;
        hsync_w -= hsync_w % CVT_H_GRANULARITY;
        mode_info->hsync_start = mode_info->hsync_end - hsync_w;

        /* Fill in vsync values */
        mode_info->vsync_start = mode_info->vdisplay + CVT_MIN_V_PORCH_RND;
        mode_info->vsync_end = mode_info->vsync_start + vsync;

    }
    else {                      /* reduced blanking */
        /* Minimum vertical blanking interval time (µs) - default 460 */
#define CVT_RB_MIN_VBLANK 460.0

        /* Fixed number of clocks for horizontal sync */
#define CVT_RB_H_SYNC 32.0

        /* Fixed number of clocks for horizontal blanking */
#define CVT_RB_H_BLANK 160.0

        /* Fixed number of lines for vertical front porch - default 3 */
#define CVT_RB_VFPORCH 3

        int vblank_interval_lines;

        /* 8. Estimate Horizontal period. */
        hperiod = ((float) (1000000.0 / vfield_rate - CVT_RB_MIN_VBLANK)) /
            (vdisplay_rnd + 2 * vmargin);

        /* 9. Find number of lines in vertical blanking */
        vblank_interval_lines = ((float) CVT_RB_MIN_VBLANK) / hperiod + 1;

        /* 10. Check if vertical blanking is sufficient */
        if (vblank_interval_lines < (CVT_RB_VFPORCH + vsync + CVT_MIN_V_BPORCH))
            vblank_interval_lines = CVT_RB_VFPORCH + vsync + CVT_MIN_V_BPORCH;

        /* 11. Find total number of lines in vertical field */
        mode_info->vtotal = vdisplay_rnd + 2 * vmargin + interlace + vblank_interval_lines;

        /* 12. Find total number of pixels in a line */
        mode_info->htotal = mode_info->hdisplay + CVT_RB_H_BLANK;

        /* Fill in HSync values */
        mode_info->hsync_end = mode_info->hdisplay + CVT_RB_H_BLANK / 2;
        mode_info->hsync_start = mode_info->hsync_end - CVT_RB_H_SYNC;

        /* Fill in vsync values */
        mode_info->vsync_start = mode_info->vdisplay + CVT_RB_VFPORCH;
        mode_info->vsync_end = mode_info->vsync_start + vsync;
    }

    /* 15/13. Find pixel clock frequency (kHz for xf86) */
    mode_info->dot_clock = mode_info->htotal * 1000.0 / hperiod;
    mode_info->dot_clock -= mode_info->dot_clock % CVT_CLOCK_STEP;

    /* 16/14. Find actual Horizontal Frequency (kHz) */
    mode_info->hsync = ((float) mode_info->dot_clock) / ((float) mode_info->htotal);

    /* 17/15. Find actual Field rate */
    mode_info->vrefresh = (1000.0 * ((float) mode_info->dot_clock)) /
        ((float) (mode_info->htotal * mode_info->vtotal));

    /* 18/16. Find actual vertical frame frequency */
    /* ignore - just set the mode flag for interlaced */
    if (interlaced)
        mode_info->vtotal *= 2;

    if (reduced)
        mode_info->mode_flags |= LIBXCVT_MODE_FLAG_HSYNC_POSITIVE | LIBXCVT_MODE_FLAG_VSYNC_NEGATIVE;
    else
        mode_info->mode_flags |= LIBXCVT_MODE_FLAG_HSYNC_NEGATIVE | LIBXCVT_MODE_FLAG_VSYNC_POSITIVE;

    if (interlaced)
        mode_info->mode_flags |= LIBXCVT_MODE_FLAG_INTERLACE;

    /* FWXGA hack adapted from hw/xfree86/modes/xf86EdidModes.c, because you can't say 1366 */
    if (mode_info->hdisplay == 1360 && mode_info->vdisplay == 768) {
         mode_info->hdisplay = 1366;
         mode_info->hsync_start--;
         mode_info->hsync_end--;
    }

    return mode_info;
}