fix bug with alpha channel not working on some nodes

lua/shaders.lua

@@ -105,6 +105,16 @@ local texturecolor_f = [[
     }
 ]]
 
+local premult_texturecolor_f = [[
+    precision mediump float;
+    uniform sampler2D tex;
+    uniform vec4 color;
+    varying vec2 v_uv;
+    void main() {
+        gl_FragColor = texture2D(tex, v_uv) * vec4(color.rgb * color.a, color.a);
+    }
+]]
+
 local sources = {
     color = {color_v, color_f},
     color2d = {color2d_v, color_f},
@@ -114,6 +124,7 @@ local sources = {
     texture2d = {texture2d_v, texture_f},
     texturecolor = {texture_v, texturecolor_f},
     texturecolor2d = {texture2d_v, texturecolor_f},
+    premult_texturecolor2d = {texture2d_v, premult_texturecolor_f},
 }
 
 am.shaders = {}

lua/shapes.lua

@@ -47,6 +47,7 @@ function am.rect(x1, y1, x2, y2, color)
     color = color or vec4(1)
     local verts = am.rect_verts_2d(x1, y1, x2, y2)
     local node = am.use_program(am.shaders.color2d)
+        ^am.blend"alpha"
         ^am.bind{
             vert = verts,
             color = color,
@@ -112,6 +113,7 @@ function am.circle(center, radius, color, sides)
         am.translate(center)
         ^am.scale(radius)
         ^am.use_program(am.shaders.color2d)
+        ^am.blend"alpha"
         ^am.bind{
             vert = verts,
             color = color,
@@ -163,6 +165,7 @@ function am.line(point1, point2, thickness, color)
     set_verts()
     local node =
         am.use_program(am.shaders.color2d)
+        ^am.blend"alpha"
         ^am.bind{
             vert = verts,
             color = color,

lua/text.lua

@@ -183,7 +183,7 @@ function am.text(font, str, color, halign, valign)
     local w, h = set_text_verts(font, str, verts, uvs, halign, valign)
     local node =
         am.blend(font.is_premult and "premult" or "alpha")
-        ^am.use_program(am.shaders.texturecolor2d)
+        ^am.use_program(font.is_premult and am.shaders.premult_texturecolor2d or am.shaders.texturecolor2d)
         ^am.bind{
             vert = verts,
             uv = uvs,
@@ -384,7 +384,7 @@ function am.sprite(image0, color, halign, valign)
     set_sprite_verts(image, verts, uvs, halign, valign)
     local node =
         am.blend(image.is_premult and "premult" or "alpha")
-        ^am.use_program(am.shaders.texturecolor2d)
+        ^am.use_program(image.is_premult and am.shaders.premult_texturecolor2d or am.shaders.texturecolor2d)
         ^am.bind{
             vert = verts,
             uv = uvs,

src/am_framebuffer.cpp

@@ -30,7 +30,7 @@ void am_framebuffer::init(lua_State *L, am_texture2d *texture, bool depth_buf, b
     if (status != AM_FRAMEBUFFER_STATUS_COMPLETE) {
         luaL_error(L, "framebuffer incomplete");
     }
-    clear_color = clear_color;
+    am_framebuffer::clear_color = clear_color;
     user_projection = false;
     float w = (float)width;
     float h = (float)height;

tests/test_render.exp

@@ -0,0 +1 @@
+ok

tests/test_render.lua

@@ -0,0 +1,73 @@
+win = am.window{}
+
+ib1 = am.image_buffer(1)
+v1 = ib1.buffer:view"ubyte"
+tx1 = am.texture2d(ib1)
+fb1 = am.framebuffer(tx1)
+
+fb1:clear()
+fb1:read_back()
+assert(v1[1] == 0)
+assert(v1[2] == 0)
+assert(v1[3] == 0)
+assert(v1[4] == 255)
+fb1.clear_color = vec4(128, 64, 32, 16) / 255
+fb1:clear()
+fb1:read_back()
+assert(v1[1] == 128)
+assert(v1[2] == 64)
+assert(v1[3] == 32)
+assert(v1[4] == 16)
+
+fb1.clear_color = vec4(0, 0, 0, 1)
+
+fb1:clear()
+fb1:render(am.rect(-2, -2, 2, 2, vec4(0, 1, 0, 1)))
+fb1:read_back()
+assert(v1[1] == 0)
+assert(v1[2] == 255)
+assert(v1[3] == 0)
+assert(v1[4] == 255)
+
+fb1:clear()
+fb1:render(am.rect(-2, -2, 2, 2, vec4(255, 255, 0, 128) / 255))
+fb1:read_back()
+assert(v1[1] == 128)
+assert(v1[2] == 128)
+assert(v1[3] == 0)
+assert(v1[4] == 64 + 255 - 128)
+
+fb1:clear()
+fb1:render(am.circle(vec2(0, 0), 2, vec4(255, 255, 255, 64) / 255))
+fb1:read_back()
+assert(v1[1] == 64)
+assert(v1[2] == 64)
+assert(v1[3] == 64)
+assert(v1[4] == 16 + 255 - 64)
+
+fb1:clear()
+fb1:render(am.line(vec2(-2, -2), vec2(2, 2), 4, vec4(255, 0, 128, 128) / 255))
+fb1:read_back()
+assert(v1[1] == 128)
+assert(v1[2] == 0)
+assert(v1[3] == 64)
+assert(v1[4] == 64 + 255 - 128)
+
+fb1:clear()
+fb1:render(am.scale(4) ^ am.text("I", vec4(255, 0, 0, 128) / 255))
+fb1:read_back()
+assert(v1[1] == 128)
+assert(v1[2] == 0)
+assert(v1[3] == 0)
+assert(v1[4] == 128 + 255 - 128)
+
+fb1:clear()
+fb1:render(am.sprite("CCC\nCCC", vec4(128, 128, 128, 128) / 255))
+fb1:read_back()
+assert(v1[1] == 0)
+assert(v1[2] == 64)
+assert(v1[3] == 64)
+assert(v1[4] == 64 + 255 - 128)
+
+win:close()
+print"ok"