From f59134d53a36e91332d3b00084b88f818295bdda Mon Sep 17 00:00:00 2001
From: John Tsiombikas <nuclear@member.fsf.org>
Date: Thu, 15 Sep 2022 18:22:21 +0300
Subject: [PATCH] initial commit

---
 .gitignore |    3 ++
 Makefile   |   12 +++++
 glpixels.c |  144 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 159 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Makefile
 create mode 100644 glpixels.c

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..198a5c8
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+*.o
+*.swp
+glpixels
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..bb38ce2
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,12 @@
+obj = glpixels.o
+bin = glpixels
+
+CFLAGS = -pedantic -Wall -g
+LDFLAGS = -lGL -lglut -lm
+
+$(bin): $(obj)
+	$(CC) -o $@ $(obj) $(LDFLAGS)
+
+.PHONY: clean
+clean:
+	rm -f $(obj) $(bin)
diff --git a/glpixels.c b/glpixels.c
new file mode 100644
index 0000000..b04ee88
--- /dev/null
+++ b/glpixels.c
@@ -0,0 +1,144 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+#include <assert.h>
+#include <GL/glut.h>
+
+enum {
+	MODE_VERTEX,
+	MODE_DRAWPIX,
+	MODE_TEXQUAD,
+	MODE_TEXTRI,
+
+	NUM_MODES
+};
+
+int init(void);
+void display(void);
+void idle(void);
+void reshape(int x, int y);
+void keyb(unsigned char key, int x, int y);
+
+int win_width, win_height;
+int max_xscroll, max_yscroll;
+
+#define IMG_W	1024
+#define IMG_H	1024
+unsigned int img[IMG_W * IMG_H];
+
+int mode = MODE_DRAWPIX;
+
+int main(int argc, char **argv)
+{
+	glutInit(&argc, argv);
+	glutInitWindowSize(800, 600);
+	glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
+	glutCreateWindow("GL pixel drawing methods");
+
+	glutDisplayFunc(display);
+	glutReshapeFunc(reshape);
+	glutKeyboardFunc(keyb);
+	glutIdleFunc(idle);
+
+	if(init() == -1) {
+		return 1;
+	}
+	glutMainLoop();
+	return 0;
+}
+
+
+int init(void)
+{
+	int i, j, xor, r, g, b;
+	unsigned int *ptr;
+	unsigned int tex;
+
+	ptr = img;
+	for(i=0; i<IMG_H; i++) {
+		for(j=0; j<IMG_W; j++) {
+			xor = i ^ j;
+			r = (xor >> 1) & 0xff;
+			g = xor & 0xff;
+			b = (xor << 1) & 0xff;
+			*ptr++ = r | (g << 8) | (b << 16);
+		}
+	}
+
+	glPixelStorei(GL_UNPACK_ROW_LENGTH, IMG_W);
+
+	win_width = glutGet(GLUT_WINDOW_WIDTH);
+	win_height = glutGet(GLUT_WINDOW_HEIGHT);
+
+	glGenTextures(1, &tex);
+	glBindTexture(GL_TEXTURE_2D, tex);
+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+	glTexImage2D(GL_TEXTURE_2D, 1, GL_RGBA, win_width, win_height, 1, GL_RGBA, GL_UNSIGNED_BYTE, 0);
+
+	return 0;
+}
+
+void display(void)
+{
+	unsigned int tm = glutGet(GLUT_ELAPSED_TIME);
+	float t = tm / 256.0f;
+	int xoffs = (int)((sin(t) * 0.5f + 0.5f) * max_xscroll);
+	int yoffs = (int)((cos(t) * 0.5f + 0.5f) * max_yscroll);
+	unsigned int *start;
+
+	switch(mode) {
+	case MODE_VERTEX:
+		/* draw with points */
+		break;
+
+	case MODE_DRAWPIX:
+		/* draw with glDrawPixels */
+		start = img + yoffs * IMG_W + xoffs;
+		glDrawPixels(win_width, win_height, GL_RGBA, GL_UNSIGNED_BYTE, start);
+		break;
+
+	case MODE_TEXQUAD:
+		/* draw with textured quad */
+		break;
+
+	case MODE_TEXTRI:
+		/* draw with textured triangle */
+		break;
+	}
+
+	glutSwapBuffers();
+	assert(glGetError() == GL_NO_ERROR);
+}
+
+void idle(void)
+{
+	glutPostRedisplay();
+}
+
+void reshape(int x, int y)
+{
+	glViewport(0, 0, x, y);
+
+	win_width = x;
+	win_height = y;
+	max_xscroll = IMG_W - win_width;
+	max_yscroll = IMG_H - win_height;
+	if(max_xscroll < 0) max_xscroll = 0;
+	if(max_yscroll < 0) max_yscroll = 0;
+}
+
+void keyb(unsigned char key, int x, int y)
+{
+	switch(key) {
+	case 27:
+		exit(0);
+
+	case ' ':
+		mode = (mode + 1) % NUM_MODES;
+		break;
+
+	default:
+		break;
+	}
+}
-- 
1.7.10.4