Add texture subsetting for texture atlas

Note that in the shader N is the number of elements within the texture
and idx is the index of the element we want to submit (starting at 0).

1 files changed, 15 insertions, 11 deletions

diff --git a/src/main.c b/src/main.c
index 0241e8f..7241409 100644
--- a/src/main.c
+++ b/src/main.c
@@ -179,7 +179,6 @@ render(Context *ctx) {
     glfwGetFramebufferSize(ctx->window, &ctx->win_width, &ctx->win_height);
     glViewport(0, 0, ctx->win_width, ctx->win_height);
 
-
     // TODO: Only need to be done once on the initialization function.
     // Prepare quad rendering.
     f32 vertices[] = {
@@ -217,19 +216,19 @@ render(Context *ctx) {
 
     // Texture atlas.
     u8 texture[] = {
-       0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
-       0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
-       0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
-       0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
-       0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
-       0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
-       0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
-       0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
+       0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+       0x00, 0x00, 0x01, 0x01, 0x01, 0x01, 0x00, 0x00, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01, 0x00, 0x00, 0x01, 0x01, 0x01, 0x01, 0x00, 0x00,
+       0x00, 0x00, 0x01, 0x00, 0x00, 0x01, 0x00, 0x00, 0x01, 0x01, 0x01, 0x01, 0x00, 0x01, 0x01, 0x01, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00,
+       0x00, 0x00, 0x01, 0x00, 0x00, 0x01, 0x00, 0x00, 0x01, 0x01, 0x01, 0x01, 0x00, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00,
+       0x00, 0x00, 0x01, 0x00, 0x00, 0x01, 0x00, 0x00, 0x01, 0x01, 0x00, 0x00, 0x00, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00,
+       0x00, 0x00, 0x01, 0x00, 0x00, 0x01, 0x00, 0x00, 0x01, 0x01, 0x01, 0x00, 0x00, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00,
+       0x00, 0x00, 0x01, 0x01, 0x01, 0x01, 0x00, 0x00, 0x01, 0x01, 0x01, 0x01, 0x00, 0x01, 0x01, 0x01, 0x00, 0x00, 0x01, 0x01, 0x01, 0x01, 0x00, 0x00,
+       0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
     };
     u32 tex_id;
     glGenTextures(1, &tex_id);
     glBindTexture(GL_TEXTURE_2D, tex_id);
-    glTexImage2D(GL_TEXTURE_2D, 0, GL_R8, 16, 8, 0, GL_RED,
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_R8, 8 * 3, 8, 0, GL_RED,
             GL_UNSIGNED_BYTE, &texture);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
@@ -244,10 +243,15 @@ render(Context *ctx) {
 "#version 330 core\n"
 "layout (location = 0) in vec2 position;\n"
 "layout (location = 1) in vec2 tex_coords;\n"
+// TODO: layout (location = 2) in u32 index;
 "out vec2 tex;\n"
 "void main() {\n"
+"    float N = 3;\n"
+"    float idx = 2;\n"
+"    float m = 1.0 / N;\n"
+"    float k = m * idx;\n"
 "    gl_Position = vec4(position.x, position.y, 0.0, 1.0);\n"
-"    tex = tex_coords;\n"
+"    tex = tex_coords * vec2(m, 1.0) + vec2(k, 0.0);\n"
 "}";
 
     // Fragment shader.